Hagger et al.

BMC Public Health (2015) 15:306

DOI 10.1186/s12889-015-1648-y

STUDY PROTOCOL Open Access

A theory-based behavior-change intervention to

reduce alcohol consumption in undergraduate
students: Trial protocol
Martin S Hagger1*†, Ging Ging Wong1† and Simon R Davey1,2

Abstract
Background: Excessive alcohol consumption on single occasions among undergraduate students is a major health
issue as research has shown this pattern of drinking to be related to maladaptive health and psychosocial
outcomes. Brief, theory-based interventions targeting motivation and self-control as behavior-change techniques
have been identified as effective means to reduce alcohol consumption, but few studies have examined the interactive
effects of these components. The aim of the present study is to develop a brief theory-based intervention using
motivational and self-control intervention techniques to reduce alcohol consumption in undergraduate students.
Methods/Design: The intervention will adopt a factorial design to test the main and interactive effects of the
techniques on alcohol consumption. Using mental simulations and the strength model of self-control as the
theoretical bases of the intervention, the study will adopt a fully randomized 2 (mental simulation: mental
simulation vs. control irrelevant visualization exercise) × 2 (self-control training: challenging Stroop task vs. easy
Stroop task) between-participants design. Non-abstinent undergraduate students aged 18 years or older will be
eligible to participate in the study. Participants will complete an initial survey including self-reported alcohol
consumption measures, measures of motivation and self- measures. Participants will be randomly allocated to
receive either a mental simulation exercise presented in print format or a control irrelevant visualization exercise.
Thereafter, participants will be randomly assigned to receive a challenging online self-control training exercise or
an easy training exercise that has little self-control demand over the course of the next four weeks. Four weeks
later participants will complete a follow-up alcohol consumption, motivation and self-control measures.
Discussion: This study will provide the first evidence for the individual and interactive effects of motivational and
self-control training techniques in an intervention to reduce alcohol consumption. It will also demonstrate the
importance of adopting multiple theoretical perspectives and a factorial design to identify the unique and interactive
impact of behavior-change techniques on health behavior.
Trial registration: The trial is registered with the Australian and New Zealand Clinical Trials Registry,
ACTRN12613000573752.
Keywords: Binge drinking, Self-control, Ego-depletion, Strength model, Mental simulations, Imagery, Motivation,
Behavior change

* Correspondence: martin.hagger@curtin.edu.au
†
Equal contributors
1
Health Psychology and Behavioural Medicine Research Group, School of
Psychology and Speech Pathology, Faculty of Health Sciences, Curtin
University, GPO Box U1987, Perth, WA 6845, Australia
Full list of author information is available at the end of the article

© 2015 Hagger et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article,
unless otherwise stated.
Hagger et al. BMC Public Health (2015) 15:306 Page 2 of 13

Background are comparatively silent on exactly what components of

Australians have high rates of alcohol consumption es- the intervention ‘work’ in terms of changing behavior
pecially among younger populations [1]. In particular, and ‘how’ the components exert their effects [20]. Recent
younger populations frequently engage in high-risk research on the components of behavioral interventions
single-session alcohol drinking, frequently termed ‘binge’ has called for better intervention designs to isolate the
drinking. A recent survey revealed that two out of five individual components or techniques that are effective
young drinkers regularly engage in binge drinking putting in bringing about a change in behavioral outcomes and
them at significantly increased risk of alcohol-related in- to explain the mechanisms behind the effects through
jury [1]. In addition, 31.7% of Australians aged 18 and19 appropriate mediator variables [21-24]. As a consequence,
years and 26.9% of Australians aged 20 to 29 years are interventions need to adopt factorial designs examining
more likely to engage in risky drinking patterns leading to individual intervention components in isolation, and in
an increased vulnerability to alcohol-related harm over synergy, to ensure that the independent and interactive ef-
their lifetime when compared with older age groups. In fects of the intervention techniques can be isolated and to
addition, excessive alcohol consumption has had a nega- include measures of the psychological components that
tive impact on Australian economic and social outcomes are proposed to mediate the effects of the intervention on
[2]. For example, treatment of alcohol-related illnesses and behavioral outcomes [18,19].
injuries is estimated to cost 14.352 billion Australian Taking these considerations into account, the aim of
dollars per year [3]. Excessive alcohol consumption is the present study is to develop a theory-based interven-
also related to maladaptive health outcomes such as tion that includes multiple intervention techniques from
diabetes, heart disease, asthma, risk of cancer, mortality, two different social psychological theories of behavior
and mental illness [1,4]. change in a randomized-controlled factorial design to re-
The problem of excessive alcohol consumption is par- duce alcohol consumption in undergraduate students.
ticularly exacerbated among student populations. Rates of The intervention will include appropriate theory-based
high-risk alcohol consumption patterns such as ‘binge’ mediator variables of target components associated with
drinking are often higher in University and college student the intervention techniques to explain the processes be-
samples compared with non-student samples of the same hind the proposed intervention effects. The intervention
age [5-7]. Research has shown that undergraduate stu- will make a unique contribution to knowledge by not
dents who consume excessive alcohol are vulnerable only demonstrating significant reduction in the primary
to profound acute and chronic harms, such as drink and secondary outcome variables, namely undergraduate
driving, substance abuse, alcohol-related injuries, vio- alcohol consumption and binge drinking occasions, but
lence, and alcohol dependence [4,8,9]. Studies have demonstrate in independent and interactive effects of
also demonstrated that undergraduate students who the intervention techniques on the outcome and the ap-
drink excessively are more likely to perform poorly in propriate mediator variables. The intervention will be
their studies [10,11] and subsequently drop out from driven by two emerging theoretical approaches relevant
university [12]. to individuals’ self-regulation of behavior, namely, the
A potential solution to reduce prevalence of excessive mental simulation approach and the strength or re-
alcohol consumption among undergraduate students is source-depletion model of self-control. In the following
the development and implementation of behavioral in- sections, we outline these theoretical approaches, high-
terventions based on social psychological theory and light their relevance to reducing alcohol consumption,
models of behavior change. Many interventions adopting and introduce the intervention components and the psy-
these kinds of approaches have been developed and ap- chological constructs that the components are hypothe-
plied to reduce alcohol consumption [13-17]. Despite sized to change and, therefore, provide a mechanistic
the relative success of these interventions, two problems explanation of the effectiveness of the intervention.
exist. First, many of the interventions adopt multiple
theories and, as a consequence, multiple intervention Imagery, mental simulations, and behavioral engagement
techniques. Although the resulting intervention may There has been a recent resurgence of interest in the
have demonstrated efficacy in changing the primary be- efficacy of visualization, rehearsal and imagery strat-
havioral outcome variable, and passed ‘fit for purpose’ egies in promoting behavior change [25,26]. The effect-
on that basis, the intervention itself is not revealing in iveness of imagery-based strategies stems from the
terms of the precise mechanism by which the interven- tenets of Bandura’s [27,28] social cognitive theory. Ac-
tion exerts its effects and does not permit the isolation cording to the theory, imagery, particularly imagining
of the individual techniques so that their relative inde- or visualizing the self engaging in a desired behavior,
pendent effectiveness on the behavioral outcome can be leads to behavior change because it provides a form of
ascertained [18,19]. This means that the interventions a ‘self-model’ or vicarious experience, which is central
Hagger et al. BMC Public Health (2015) 15:306 Page 3 of 13

to the development of self-efficacy. Self-efficacy is, evidence to support the effectiveness of imagery-based in-
therefore, one potential mechanism by which such im- terventions such as mental simulations on health related
agery strategies affect a change in behavior. Another behavior. On the proposed mechanisms, however, the evi-
mechanism by which imagery-based techniques may dence is less conclusive with motivation and self-efficacy as
promote behavioral engagement is through promoting identified as possible mechanisms for mental simulation
greater importance of the goal [25,26] and promoting effects.
better accessibility of cues to action and goals [29,30].
One class of imagery-based intervention techniques is The ‘Strength’ or ‘Resource Depletion’ Model of Self-
mental simulations, which are defined as imagining and control
rehearsing future events. There are two kinds of mental Self-control is another construct that has been identified
simulations: outcome simulation and process simulation. as an important factor associated with the regulation of
Outcome simulation involves imagining attainment of a health-related behavior [62-64]. Self-control is defined as
targeted goal while process simulation requires imagin- the capacity to control or regulate impulses, temptations,
ing and rehearsing the steps required to achieve the goal or ‘dominant’ responses and to overcome well-learned,
[31]. Mental simulations have been shown to be effective ingrained habitual actions for some goal-directed alterna-
in evoking behavior change in diverse contexts such as tive [65-72]. Much of the research on self-control in health
studying for exams [31], fruit consumption [30], domains has focused on trait conceptualizations of self-
intention to buy a product [32], anxiety reduction [33], control and has demonstrated that good’ self-control is
and alcohol consumption [34]. The effect sizes of mental associated with numerous adaptive health-related behaviors
simulation interventions is generally small-to-medium, and outcomes [62,73-77].
with a medium effect size reported for the research on An alternative perspective on self-control is offered by
alcohol consumption of employees, the context that is the ‘strength’ or resource depletion model which concep-
most closely aligned to that of the current study [34]. tualizes self-control as limited resource that permits in-
The effect size is comparable with the effect sizes of dividuals to engage in acts of self-control, but only for a
intervention techniques designed to change intentions finite period after which the resource becomes depleted
[35] and self-efficacy [36] in research on health behavior leading to impaired self-control capacity unless an indi-
change. vidual is able to rest and recover [64,78-80]. The state of
A key approach to understanding intervention effect- reduced self-control capacity or ‘strength’ is known as
iveness is to identify the psychological variables that me- ego-depletion. Research adopting the model has typically
diate the effects of interventions on behavioral outcomes adopted an experimental procedure, known as the dual
[37,38]. Researchers have turned to social cognitive task paradigm, to test model effects [78,81]. The para-
[39-46] and integrated models of motivation [18,47-56] digm requires individuals to engage in two consecutive
in order to identify the key mediators of interventions. tasks, for experimental group participants both tasks re-
Research has suggested that imagery-based and mental quire self-control while for control group participants
simulation intervention techniques in health behavior only the second task requires self-control. To the extent
exert their effects through changes in motivation [30,57], that experimental participants’ performance on the second
intentions and attitudes [33,58] and planning [31], al- self-control task is impaired, we have sharp confirmation
though there are few studies that have conducted formal of the ego-depletion effect. Research has supported the
mediator analyses. Knauper et al. [30] revealed that the ef- ego-depletion effect across multiple studies and has shown
fectiveness of a mental imagery intervention was mediated that the depletion effect occurs for tasks in multiple
by motivation and Pham and Taylor [31] demonstrated domains of self-control indicating that the resource is a
that planning was a key mediator of the effect of mental unitary, generalized effect rather one that is confined to
simulations on studying behavior, which is highly salient particular tasks [63,70,81-83].
given increased recent interest in planning interventions in An important additional hypothesis derived from the
health contexts [59]. Interestingly, no studies have found strength model is the training effect. A growing number
self-efficacy to be a mediator of the effects of imagery on of studies have demonstrated that repeated practice on
behavior despite hypothesizing it as a theoretically-relevant self-control tasks improves regulatory capacity. According
mediator, measuring the construct and including it as a to the strength model, engaging in tasks that demand
mediator in analyses [30,33,57]. Research in other domains, self-control on a regular basis can improve self-control
such as injury prevention, have found effects for imagery capacity by ‘building up’ additional resources that can
interventions on self-efficacy and behavioral outcomes, im- be made available or by making the application of the re-
plicating it in the process by which imagining processes source more efficient [84]. Research has demonstrated
and outcomes may effect behavior change [60,61]. Overall, that regular practice on self-control tasks in laboratory
research in the health domain has presented consistent and field settings leads to better performance on self-
Hagger et al. BMC Public Health (2015) 15:306 Page 4 of 13

control tasks in the laboratory [84-86] as well as health- abroad impact on behaviors that are dependent on such
related behaviors requiring self-control [87-90] including automatic processes [69,72]. This proposition is consistent
alcohol consumption [91-93]. The strength of self-control with recent trends in theory on behavioral enactment
training effects has been shown to be of medium effect which indicate that actions are controlled by two systems:
size which is comparable to other interventions such as reflective and impulsive [97]. The reflective system is a de-
those targeting intention [35] and self-efficacy [36]. For liberative pathway to action in which individuals decide
example, a meta-analysis of self-control training on on a course of action as a result of conscious consideration
self-control task performance found a medium-sized effect of the costs, benefits, consequences and outcomes of the
[81] and a recent meta-analysis of response-inhibition action. Such a system is controlled, slow, reasoned, and
training, using similar tasks to those used in the current conscious, often termed a ‘cool’ system by some theorists
study, on health behavior found a small-to-medium sized [98]. This is contrasted with the impulsive system which is
effect [94]. a more spontaneous, automatic pathway to action in
Training studies have demonstrated that the practice which individuals act in response to well-learned cues or
of self-control promotes behavior change in a number of heuristics that require little conscious involvement or de-
contexts, providing indication of the generalized, unitary liberation. The impulsive system is fast, non-conscious,
nature of self-control resources [85,87,93]. However, a and automated and often referred to as a ‘hot’ system [98].
key unresolved issue is the mechanism that drives the As actions controlled by the impulsive system often
direction and allocation of self-control resources to in- occur outside the individual’s awareness and in responses
crease behavioral enactment. It is unlikely that individuals to well-learned cue-response pairings, it is difficult to over-
will commit self-control resources toward engaging in be- ride and change such actions i.e. to break the cue-response
haviors for which they have no motivation. The resources link. It often takes considerable self-control or capacity to
would more likely be allocated elsewhere, such as toward inhibit responses to overcome the automated link. From
enacting behaviors that they are motivated to perform. the perspective of the strength model, self-control, that is
This gives rise to the possibility is that behavior change the capacity to inhibit the automated response, is a limited
will be more effective if participants can direct their self- resource permitting individuals to inhibit their responses
control efforts towards a particular target behavior for for a finite period until the resource becomes depleted
which they are highly motivated [95,96]. Interventions limiting subsequent capacity for inhibition. An important
might, therefore, be more effective if means to increase feature of the self-control ‘resource’ is that it is ‘domain
motivation toward behaviors could be delivered alongside general’ i.e. it is a generalizable resource that enables indi-
the practice on self-control tasks in a factorial design viduals to control their behavior in multiple domains. This
giving participants the opportunity and drive to direct has been shown in many studies in which individuals
their self-control resources toward that specific behavior. engaged in a task that requires them to inhibit their
Instilling increased motivation may, therefore, be effective self-control in one domain results in impaired response
in focusing individuals on directing their self-control inhibition in another. Importantly in the current context,
resources towards specific target behavior. exerting self-control on laboratory-based tasks that require
the inhibition of responses leads to reduced capacity to in-
The current research hibit responses when presented with tempting behaviors in
The purpose of the current research is to develop a brief health-related domains such as resisting alcohol in social
theory-based intervention adopting imagery-based motiv- drinkers or tempting foods in people with low eating re-
ational and self-control training behavior-change compo- straint. Consistent with this line of research, studies have
nents and a randomized controlled factorial-design that revealed that training on tasks that require self-control i.e.
will lead to a reduction in alcohol consumption among the ability to inhibit responses will improve response
undergraduate students, an at-risk population, over a four- inhibition capacity and provide individuals to inhibit
week period. We expect that the influence of motivational cue-response pairings more effectively. And this effect
and self-control components on promoting alcohol re- also appears to be domain general, consistent with the
duction will interact, such that individuals who are strength model [78] and the reflective-impulsive model
both motivated and provided with training to enhance [97]. Training on self-control tasks which require regular
their self-regulatory capacity will exhibit the greatest inhibition of a pre-potent response is, therefore, hypothe-
reduction in their alcohol consumption. Why would train- sised to improve generalized capacity for self-control as
ing self-control improve an individual’s capacity to reduce shown in previous studies [84,88]. With individuals who
their future alcohol consumption? Our position is that have sufficient motivation to reduce their alcohol intake,
training individuals to inhibit well-learned, ingrained re- improving response inhibition capacity is expected to im-
sponses with little cognitive control or conscious thought prove capacity to inhibit the temptation to drink. This
(i.e., so called ‘automatic’ or ‘habitual’ behaviors) will have may be relevant in situations where they may be tempted
Hagger et al. BMC Public Health (2015) 15:306 Page 5 of 13

to drink more than usual. They can therefore bring their as consuming more than 4 standard drinks on a single
improved generalized capacity to bear on reducing their drinking occasion by the NHMRC [4], is related to sub-
alcohol consumption is situations where they may be stantially increased health risks such as unintentional
tempted to drink to excess. Their additional response injury, increased probability of unplanned and unpro-
inhibition capability afforded to them by virtue of the tected sexual intercourse, and risk of being involved in
training would provide sufficient capacity to override the violence and social disorder [9,99,100]. Given that stu-
automatic, cue-driven response to stimuli to drink alcohol. dents are more likely to engage in binge drinking than
We therefore propose that self-control training will only their non-student peers [10,101], binge drinking is con-
have a substantive effect on behavioral outcomes if individ- sidered an important risk factor for alcohol-related
uals are motivated to change their behavior. Participants harm specific to this population. We will, therefore, include
whose self-control capacity has been trained, but have little a secondary outcome variable, frequency of occasions of
or no motivation to reduce their alcohol consumption are binge drinking, self-reported by participants to account for
less likely to direct the increased self-control capacity this risky pattern of alcohol consumption that is likely to
gleaned from training toward that particular behavior. be endemic in this population. The variable is defined as
They may direct their efforts toward behaviors to which the number of single occasions in which an individual’s
they are more motivated instead. We therefore expect that alcohol consumption exceeded 4 standard drinks [4].
the combined manipulation of self-control training and The intervention will comprise two components, mo-
motivational imagery-based intervention components, tivational and self-control training. The motivational
namely, mental simulations, to be more effective in component of the intervention will comprise a process
changing behavior than either of the components alone. and outcome mental simulation manipulation in which
Importantly, the factorial design adopted in the present participants will be required to visualize the steps they
study permits the evaluation of the independent and need to take in order to reduce keep their alcohol con-
synergistic effects of each of the intervention components sumption within guideline limits in the next four weeks
on alcohol consumption. In addition, we expect the inter- and the outcomes they will achieve. This task has been
vention to be highly acceptable for use in public health adopted in previous studies and the standardized protocol
promotion campaigns due to its low response burden and adopted in these studies will be used [34]. Participants not
highly practical, accessible, and cost-effective means of de- allocated to receive the motivational intervention compo-
livering the intervention. nent will receive an irrelevant visualization task. The
We will administer outcome measures of two forms of self-control training component will require partici-
alcohol consumption in the current research: total alcohol pants to engage in an online Stroop color-naming task
consumption and frequency of ‘binge’ drinking. Our pri- delivered online either by smartphone or personal com-
mary outcome variable in the current research is overall puter for the duration of the subsequent four-week period.
self-reported alcohol consumption by undergraduate stu- The Stroop task was developed and piloted previously and
dents. We cannot expect students to curb their alcohol has been shown to effectively enhance self-control cap-
drinking altogether, so the target outcome identified for acity over a four-week training period [85]. Participants
participants in the current study will be keeping alcohol allocated to the self-control training condition will receive
consumption within the guideline limits specified by the a ‘challenging’ version of the Stroop task while participants
Australia National Health and Medical Research Council in the control condition will receive an ‘easy’ version,
(NHMRC). The NHMRC guideline limits on safe alcohol which is not expected to lead to any substantive improve-
consumption are 14 standard drinks (each standard drink ments on self-control capacity.
is equivalent to 12.5 ml of pure alcohol) per week. The
guideline limits will be clearly outlined to participants in Methods
advance of the research commencing and our purpose Study design
was to ensure that students did not exceed this limit as it The research will adopt a fully randomized-controlled 2
is associated with long-term (chronic) harm [4]. We do, (mental simulation: mental simulation vs. control irrelevant
however, recognise that the guidelines reflect limits aimed visualization exercise) × 2 (self-control training: challen-
at reducing chronic harm and that other patterns of alco- ging Stroop task vs. easy Stroop task) between-participants
hol consumption prevalent in students may also present a factorial design. Mental simulation and self-control train-
serious threat to health. For example, the consumption of ing manipulations will be the independent variables while
14 standard drinks on a single occasion, once per week self-reported alcohol consumption collected four-weeks
may mean that an individual’s consumption falls within after the initiation of the intervention will be the primary
NHMRC overall guideline limits, but would constitute dependent variable. Baseline alcohol consumption and trait
increased risk of acute harm. High-risk single-session alco- self-control will be included as covariates. Participants will
hol consumption, also known as ‘binge’ drinking, defined be randomly allocated to one of the four intervention
Hagger et al. BMC Public Health (2015) 15:306 Page 6 of 13

conditions according to a schedule generated by an online prize draw for shopping vouchers. The study is described
experimental randomising tool [102]. A participant flow as an intervention to reduce alcohol consumption. As-
diagram and overview of study design is provided in suming a medium effect size for mental simulation in-
Figure 1. The study protocol has been submitted to, terventions on behavior reported by Pham and Taylor
reviewed, and approved by Curtin University Human [31] (d = 0.56) and an effect size of similar magnitude
Research Ethics Committee. for the effects of self-control resource training reported
in Hagger et al.’s [81] meta-analysis (d = .62), a power
Participants analysis using G*Power v3.1 [104] setting power at .80
Participants will be undergraduate students from a large and alpha at .05, estimates that we will require a total
University in Western Australia. Students will be eligible to sample size of between 120 and 144 participants with
participate if that are 18 years or older and non-abstinent between 30 and 36 participants in each intervention
with respect to alcohol consumption to be eligible to group. The variation in the sample size estimate is due
participate in the study. Participants will be excluded if to the use of the two different effect sizes to compute
they are heavy or dependent drinkers as identified by the power analysis, each of which gives a slightly different
the Fast Alcohol Screening Test (FAST) [103]. Participants result.
will be recruited using email circular and notice board
advertisements distributed throughout the University and Procedure
from a dedicated participant pool for undergraduate On recruitment, participants will be required to attend
psychology students incentivised by course credit or a an initial laboratory session with the experimenter at a

Participants identified as eligible and Ineligible (not under 18 or

randomized to conditions abstinent) or declined to
participate

Allocated to conditions using block

randomization procedure (N = 120)

Allocated to Allocated to Allocated to Allocated to

control (irrelevant mental simulation challenging self- mental simulation
visualization condition at control training and challenging
Baseline exercise, easy self- baseline (n = 30) condition at self-control
control training) baseline (n = 30) training condition
condition at at baseline (n = 30)
baseline (n = 30)

Participants receive study information and baseline measures of alcohol consumption and
psychological mediators

Participants Participants receive Participants receive Participants

receive irrelevant mental simulation irrelevant receive mental
visualization exercise visualization simulation exercise
exercise exercise

Participants Participants receive Participants receive Participants

receive easy easy (congruent) challenging receive challenging
(congruent) Stroop Stroop task for 4 (incongruent) (incongruent)
Follow- task for 4 weeks weeks Stroop task for 4 Stroop task for 4
up weeks weeks

Participants receive follow-up measures of alcohol consumption and psychological mediators

Figure 1 Trial Flowchart. The diagram illustrates the flow of participants through the proposed intervention.
Hagger et al. BMC Public Health (2015) 15:306 Page 7 of 13

mutually agreed time. Participants will be provided cinema or shopping centre. They will also be asked to
with an information sheet outlining their expectations write down their experiences on the sheet provided. The
and given the opportunity to ask questions about study purpose of the control task is to maintain an equivalent in-
requirements prior to completing and signing a consent formation load to the participants allocated to the mental
form. They will then be asked to complete a brief simulation condition.
demographic questionnaire and baseline self-report
measures of alcohol consumption and psychological Self-control training
mediator variables. Next, participants will be given an We will use regular practice on an online version of the
envelope corresponding to the condition to which they Stroop color-naming task which will be delivered on the
have been allocated that contains instructions for the participant’s smartphone as a means to train and improve
mental simulation or control manipulations. The enve- self-control resource capacity. As a fall back, in case the
lopes will be prepared by an independent researcher participant does not have access to a smartphone or does
using coded labels to represent the mental simulation not own a smartphone, we will give participants the op-
manipulation and control irrelevant visualization task portunity to conduct their self-control training on their
so that the experimenter will be blind to the intervention personal computer using their web browser. Participants
conditions until the end of the study. All participants will will be randomly allocated to an intervention group that
be presented with a written script with a generic introduc- engages in practice on using a ‘challenging’ version of the
tion section providing a brief rationale for changing their Stroop task for the duration of the intervention while par-
alcohol behavior. The instructions will inform participants ticipants allocated to the comparison group will engage in
that the purpose of the study is to keep their alcohol regular practice on an ‘easy’ version of the task that is not
consumption within nationally-recognized ‘safe’ guideline proposed to have any substantive effect on training self-
limits to promote better health and reduce adverse effects. control. Participants will practice on the task twice per
A definition of NHMRC guideline limit for alcohol con- day for the four weeks duration of the intervention. The
sumption of 14 standard drinks per week, a definition of a tasks are similar to those developed for use in a previous
standard drink, and examples of volumes and measures of study [85]. The challenging version of the task requires
typical drinks that constitute a standard drink will be pro- participants to respond to a series of word items in which
vided. This will be followed by instructions for the mental the word meaning and the color of the ink in which it is
simulation or control irrelevant visualization exercise written are incongruent (e.g., the word “green” written in
according to the randomly-allocated trial condition (see red ink). The easy version is modified such that the word
Additional file 1). meaning and ink colour are congruent. There are equal
numbers of word items with four possible colors (“red”,
Mental simulation intervention “green”, “yellow”, and “blue”) presented in random order.
Participants randomized to the mental simulation inter- Participants will be given instructions on how to perform
vention, will be presented with written instructions in the the task on a smartphone or personal computer during
form of a standardized script for the mental simulation ex- the initial visit to the laboratory. Participants will be of-
ercise (Additional file 1). Participants will be instructed to fered the opportunity to use a generic smartphone loaned
imagine the steps they will take to reduce their alcohol to them by the experimental team, their own smartphone,
consumption and the salient outcomes they expect to or their personal computer to engage in the training tasks.
achieve. The instructions will be adapted from Pham and Participants will be given ample opportunity to familiarize
Taylor’s [31] ‘process’ and ‘outcome’ mental simulation themselves with the task and to ask any questions. Partici-
scripts. Participants will be required to follow the instruc- pants will be informed that they will be prompted to
tions on the sheet and perform the metal simulation exer- engage in the task via a text message sent to their
cise with their eyes closed. Then they will be asked to smartphone or an email to their regular email address
write about their experience with the visualization exercise containing a URL link. Upon clicking the URL link,
in the space provided on the sheet and to memorize it. participants will be directed to a website to complete
Written responses will be content analysed to check for the version of Stroop color-naming task corresponding
compliance with the task. The exercise is expected to take to the condition to which they will be allocated. Partici-
no longer than 10 minutes. Participants randomized to pants will be presented with a series of 238 color-word
the control condition will receive written instructions in items presented in seven 34-item blocks on their screen
the form of a standardized script for an irrelevant with each item presented for 2000 milliseconds (ms).
visualization exercise identical in procedure to the mental Participants will use a response panel presented on the
simulation exercise (Additional file 1). Instead of visualiz- smartphone touchscreen or their computer keyboard to
ing reducing their alcohol consumption, however, partici- identify the colour in which the word is written rather
pants will be required to imagine a recent visit to the than respond to the word meaning. Participants will
Hagger et al. BMC Public Health (2015) 15:306 Page 8 of 13

have 800 ms to provide a response by choosing the will be excluded from the study prior to engaging in the
colour-word response options. Response latencies for each protocol. Participants identified as heavy or dependent
item will be logged along with errors. If no response is drinkers by the FAST will be provided with a leaflet provid-
given, the response will be logged as “unanswered” and ing advice on how to seek professional help for their alco-
the next colour-word item will be presented. hol consumption.
The Stroop task is expected to approximately 5 minutes.
Participants will complete the task to which they have Measures of psychological mediator variables
been assigned immediately after the mental simulation In keeping with research examining the effects of the
task in the initial session and then repeat the Stroop task intervention components on behavior, we will include
twice per day when prompted, at 7 am and 5 pm, through- measures of key psychological variables that are likely to
out the four-week intervention period. All participants’ mediate the impact of the motivational and self-control
Stroop data will be uploaded to, and stored on, a remote intervention techniques on alcohol consumption. Mental
computer server for subsequent retrieval to compliance simulations are likely to be mediated by social cognitive
analysis. variables related to motivation. In keeping with previous
Participants will be reminded to practice the Stroop research that has demonstrated significant effects of
task once per week via emails and/or text messages mental simulations on variables form the theory of
throughout the four-week intervention period. After four planned behavior, we will measure participants’ inten-
weeks participants will be sent a series of reminder tions, attitudes, perceived behavioral control, and sub-
emails to prompt them to complete follow-up dependent jective norms toward alcohol consumption. Standardized
measures of self-reported alcohol consumption and measures of the theory of planned behavior constructs
follow-up measures of psychological mediator variables, used in previous studies will be adopted [42,107]. Inten-
identical to those administered at baseline. Thereafter, tions will be assessed with three items (e.g. “I intend to
participants will receive a full debrief and provided with keep my alcohol drinking to within safe limits on each
an opportunity to receive the final group-level results of individual occasion or session over the next four weeks”)
the intervention. rated on six-point Likert-type scales ranging from 1 (ex-
tremely unlikely) to 6 (extremely likely). Attitudes will be
Primary and secondary outcome measures assessed using five semantic-differential items (e.g. enjoy-
Our primary outcome measure is participants’ self- able-unenjoyable, important-unimportant) on six-point
reported alcohol consumption over the previous four scales in response to a common stem (“For me, keeping
weeks consistent with NHMRC guidelines [4]. Our sec- my alcohol drinking to within safe limits on each indi-
ondary dependent variable is participants’ self-reported vidual occasion or session over the next four weeks
number of binge drinking occasions over the previous four is…”). Perceived behavioral control will be measured
weeks. Both primary and secondary outcome measures will using three items (e.g. “How confident are you that you
administered at baseline and at follow-up. Participants will can keep your alcohol drinking to within safe limits on
be asked to recall and report the absolute number of stand- each individual occasion or session over the next four
ard drinks they had consumed and the number of occa- weeks?”) on six-point Likert-type scales ranging from 1
sions when they engaged in binge drinking, that is, (no control at all) to 6 (complete control). Subjective
exceeding more than 4 standard drinks on a single drink- norms will be assessed using three items (e.g. “Most
ing occasion, per week over the previous four weeks people I know would approve of me keeping my alcohol
[34,105]. The self-report measures are based on the drinking to within safe limits on each individual occa-
time-line follow back technique which has been shown sion or session over the next four weeks.”) on six-point
to provide precise estimates of alcohol drinking [106]. Likert-type scales ranging from 1 (disagree) to 6 (agree).
This measure uses a number of techniques to aid recall We will also assess generalized motivation to reduce
such as linking alcohol drinking with significant events. alcohol consumption based on measures identified in
In addition, the FAST will be administered to students previous research [34,107,108]. The motivation measure
recruited to the study at baseline [103]. The measure will adopt three items (e.g. “How motivated are you to
comprises four items (e.g. “How often during the last keep your alcohol drinking to within safe limits on each in-
year have you failed to do what was normally expected dividual occasion or session over the next four weeks?”)
of you because of drinking?”) and has demonstrated with responses made on six-point Likert-type scales ranging
adequate validity and reliability to assess the extent of from 1 (not at all motivated) to 6 (extremely motivated).
heavy and dependent drinking. FAST scores will be We also expect that the effect of self-control training
used as a means to screen participants for heavy alcohol on alcohol consumption will be mediated by perceptions
consumption that is indicative of alcohol dependency. of subjective self-control capacity. We will therefore in-
Participants identified as heavy or dependent drinkers clude a modified self-report measure of self-control to
Hagger et al. BMC Public Health (2015) 15:306 Page 9 of 13

reflect current self-control capacity. Specifically, we will baseline alcohol consumption and trait self-control as
adopt the state self-control capacity scale to measure covariates. The analysis permits the main and interactive
participants current self-control reserve (Ciarocco, effects of mental simulation and self-control training inter-
Twenge, Muraven, & Tice, 2011). The scale comprises vention components. We predict statistically-significant
25-items (e.g., “I feel discouraged”) assessed on seven- main effects of medium size of mental simulation and
point Likert-type scales ranging from 1 (not true) to 7 self-control training on alcohol consumption, but also ex-
(very true). In addition, we will assess dispositional levels pect a statistically-significant, medium-sized interaction
of self-control using Tangney et al.’s [73] self-control effect such that participants receiving the mental simula-
questionnaire. The short version of the scale will be used tion and challenging self-control training components will
which comprises 13-items (e.g., “I am lazy”) assessed on report significantly lower levels of alcohol consumption
five-point Likert scales ranging from 1 (not true at all) than participants receiving either of the intervention com-
to 5 (very true). The trait scale will only be administered ponents alone and participants that received neither
to participants in the introductory session and not at manipulation.
follow-up. We will also conduct mediation analyses to evaluate
the effectiveness of the intervention components on
Data analysis alcohol consumption. This will be conducted using
The first part of the intervention will involve testing moderated linear regression analyses with indirect
intervention compliance. We will evaluate participants’ effects reproduced using Preacher, Curran, and Bauer’s
compliance with the mental simulation manipulation by [110] asymptotic bootstrapped algorithms and the bias-
conducting a content analysis of participants’ scripts corrected bootstrap confidence interval to assess the
written during the course of the intervention. We will statistical significance of the effects [111]. Specifically,
evaluate compliance with the self-control training by we will develop binary dummy-coded variables to repre-
examining participants’ level of engagement with the sent the effects of the mental simulation (1 = received
Stroop tasks administered over the course of the four- mental simulation, 0 = received irrelevant visualization
week intervention period. The use of online delivery of strategy) and self-control training (1 = received challenging
the self-control training intervention will enable us to Stroop task, 0 = received easy Stroop task) interventions
analyze the percentage compliance with the task (including with an additional variable computed to represent the
feigned compliance, engaging in the task but providing interaction of the two. The primary outcome variable,
meaningless responses) and any improvements in Stroop follow-up alcohol consumption, will be regressed on these
performance over the course of the intervention relative to coded variables in the first instance to ascertain direct
baseline. This will also enable us to evaluate whether there effects. This will be followed by analyses including mul-
were differences in compliance across the challenging and tiple mediators of the effects including residualized
easy self-control tasks. Similar to previous studies change scores for the baseline and follow-up measures
[14,34,108,109], we will conduct a 2 (self-control training: of the theory of planned behavior variables (intentions,
challenging vs. easy) × 4 (test week: 1, 2, 3 or 4) mixed- subjective norms, attitudes, perceived behavioral control)
model ANOVA with repeated measures on the second and motivation as mediators of the mental simulation inter-
factor to test for changes in Stroop performance over vention and residualized change scores in state perceived
the course of the intervention. We will use averaged self-control between baseline and follow-up as a mediator
weekly Stroop response latencies as the dependent vari- of the effect of the self-control training intervention. The
able and hypothesize statistically-significant differences of unstandardized effects and confidence intervals will be used
medium effect sizes across intervention groups with lon- as input for Preacher et al.’s [110] bootstrapped algorithm
ger latencies for participants receiving the challenging computational tool to compute the indirect effects. We
Stroop task, but we expect a statistically-significant train- predict statistically-significant, medium-sized multiple
ing condition by time interaction effect of medium size mediation of the effects of the mental simulation inter-
such that the differences diminish over the course of the vention on follow-up alcohol consumption by the theory
intervention as participants receiving the challenging task of planned behavior and motivational change scores and
improve their self-control while participants receiving the significant mediation of the effect of self-control training
easy task exhibit little or no improvement. on alcohol consumption by state self-control change
Data on the primary dependent variable of alcohol scores. Trait self-control will be included in the analyses
consumption will be analysed using a 2 (mental simulation: as a control variable.
mental simulation vs. no mental simulation) × 2 (self-
control training: challenging vs. easy) factorial between- Discussion
participants analysis of covariance (ANCOVA) with alcohol Excessive consumption of alcohol among young people
consumption at follow-up as the dependent variable and has been recognized as a significant public health issue
Hagger et al. BMC Public Health (2015) 15:306 Page 10 of 13

due to its association with numerous health, social, and related variables beyond that which can be inferred from
economic problems [1]. Undergraduate students tend to correlational [113] and panel [114] designs.
be a particularly high-risk group as they frequently en-
gage in risky patterns of alcohol consumption such as Implications
binge-drinking [5-7]. Behavioral interventions have been
The proposed study has important implications for public
shown to be effective in reducing alcohol consumption
health specialists and researchers designing behavioral
in young people e.g., [14,108], but few have reported the interventions. The research is relevant to specialists in
theoretical basis of the intervention and its components,
public health because it will demonstrate the effective-
tested the independent and interactive effects of the
ness of brief interventions including motivational and
techniques aimed at reducing alcohol consumption, and self-control training components in reducing under-
identified they key mediators of the intervention effects.
graduate students’ alcohol consumption, the primary
The present study aims to conduct a four-week
outcome variable. This is likely to contribute to initiatives
theory-based intervention using leading behavior-change to reduce maladaptive outcomes associated with excessive
techniques to reduce alcohol consumption at follow-up
alcohol consumption in this population. Importantly, the
among undergraduate students. The intervention will
intervention techniques have low response burden and
adopt motivational and self-control training behavior- cost and are administered using efficient and effective de-
change techniques derived from psychological theory
livery methods that are readily available including the
and use a randomized-controlled factorial design to
internet and smartphones. The research is of interest to
examine the unique and interactive effect of each tech- researchers as it will provide detail on the individual and
nique in on alcohol consumption. According to theory,
interactive components of motivational and self-control
we hypothesize that participants receiving both interven-
training on alcohol consumption and also demonstrate
tion components should exhibit the lowest levels of alcohol the key mediators of the effects. This is important as it will
consumption at follow-up relative to participants receiving
assist in elucidating the ‘active ingredients’ of the interven-
each of the intervention conditions alone and participants
tion and the mechanisms by which they exert their effects.
receiving neither of the components. In addition, the re-
search will also evaluate the theoretically-relevant mediat-
ing variables that explain the effect of the motivational and Additional file
self-control training intervention components on alcohol
Additional file 1: Intervention materials including introduction,
consumption. Specifically, we expect the motivational
mental simulation, and irrelevant visualization scripts.
intervention component to be mediated by social cognitive
variables including intentions, attitudes, and motivation
and the self-control intervention to be mediated by per- Abbreviations
NHMRC: National health and medical research council; FAST: Fast alcohol
ceived self-control resource availability. screening test.
The research will make a unique contribution to
knowledge regarding interventions to reduce alcohol Competing interests
consumption and binge drinking occasions in under- There are no competing interests in relation to the study. No external
funding has been received for the conduct of the study.
graduate students because it will (a) address the limita-
tions of previous research using multiple intervention
Authors’ contributions
techniques concurrently by identifying the unique and MSH conceived the study, developed the protocol and methods, and took a
interactive effects of two isolated and independent inter- lead role in drafting the manuscript. GGW assisted with the conceiving the
vention techniques (mental simulation and self-control study, helped develop the protocol and methods, and took a lead role in
drafting the manuscript. SRD assisted with developing the methodological
training) to reduce alcohol consumption through the use protocol of the study and in revising the manuscript. All authors read and
of a factorial design [20,112]; (b) assist in identifying the approved the final manuscript.
mechanisms behind motivational and self-control training
components and their interaction on alcohol consumption Acknowledgements
by testing the effects of key proposed mediating variables We thank Jo Cranwell for her assistance with the methodological details of
the Stroop color-naming task.
[18]; (c) adopt methods that allow for the efficacy of the
intervention to be evaluated including written responses Author details
1
to the mental simulation motivational intervention [108] Health Psychology and Behavioural Medicine Research Group, School of
Psychology and Speech Pathology, Faculty of Health Sciences, Curtin
and using an objective means to manage compliance with University, GPO Box U1987, Perth, WA 6845, Australia. 2Department of
the programme of self-control resource training via an on- Psychology, University of Hertfordshire, Hatfield, Hertfordshire, United
line training task [85]; and (d) extend knowledge of the Kingdom.
causal effects of an intervention aimed at affecting change Received: 29 September 2013 Accepted: 17 March 2015
in health behavior through motivational and self-control
Hagger et al. BMC Public Health (2015) 15:306 Page 11 of 13

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