Beha. Ru. 77~. Vol. 28. No. 4. pp. 341-345. 1990 GOO5-7967/90$3.00 + 0.

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Obsessions and compulsions: psychometric properties of the Padua Inventory with an

American college population

LEE G. STERNBERGER and G. LEONARD BURNS*

Department of Psychology, Washington State University, Pullman, WA 991644820, U.S.A

(Receiced 22 February 1990)

Summary-The psychometric properties of the Padua inventory, a self-report measure of obsessive-

compulsive behaviors, were examined in a sample of 678 American college students. Results showed eood
internal consistency as well as convergent and divergent validity with the subscales of the Symptom
Checklist-90 Revised and the Maudsley Obsessional-Comoulsive Inventorv. A orincioal
r~ r~ comnonents
r -~-~---
analysis suggested a four factor solution (i.e. ‘impaired control of mental acti&ies’. ‘checking’. ‘urges and
worries of losing control of motor behaviors’, and ‘being contaminated’). The factor structure was very
similar to that found in the original Italian study of the inventory. Suggestions are made for the use of
the Padua Inventory in the study of obsessions and compulsions in nonclinical samples.

A variety of measurement procedures exist for the assessment of obsessive-compulsive disorder (Mavissakalina & Barlow,
1981). Of the available self-report inventories, the Compulsive Activity Checklist (CAC) (Freund, Steketee & Foa, 1987)
and the Maudsley Obsessional-Compulsive Inventory (MOCI) (Hodgson & Rachman. 1977) are the two most widely used
instruments to measure obsessive-compulsive symptoms. The CAC measures the degree to which compulsive behaviors
interfere with daily activities, while the MOCI measures the severity of obsessive-compulsive behaviors. Research indicates
that both measures have good psychometric properties with clinical and nonclinical samples (Cottraux, Bouvard, Defayolle
& Messy. 1988; Foa, Steketee, Grayson, Turner & Latimer, 1984; Insel, Murphy, Cohen, Alterman, Kilton & Linnoila,
1983: Marks. Stern. Marison. Cobb & McDonald, 1980: Perse. Greist. Jefferson, Rosenfield & Dar. 1987: Sanvio & Vidotto.
1985; Sternberger & Burns, 1990).
Sanavio (1988) recently developed a new self-report measure of obsessions and compulsions. This measure, the Padua
Inventory (PI), assesses the degree of disturbance or difficulty which 60 thoughts and behaviors engender for the individual.
Subsequent to careful test development procedures, Sanavio (1988) presented initial standardization data on the inventory
and its psychometric properties for three samples of Italians. The standardization data was reported on a group of 967
Italians between the ages of 16-70 and the second two samples (approx. 200 Italian college students in each) examined the
new inventory’s test-retest reliability and correlations with other measures of anxiety and obsessions<ompulsions. The
results indicated that PI demonstrated good reliability (internal consistency and stability over a 30-day interval) as well
as convergent/divergent and discriminative validity. In regard to discriminative validity, individuals with a DSM-III
diagnosis of obsessive<ompulsive disorder scored significantly higher on the PI than a group of individuals with other
disorders (agoraphobia, social phobia, depression and psychosexual dysfunction).
Compared to the earlier studies on the CAC and MOCI, which have only found strong contamination (washing) and
checking factors, the principal components analysis of the PI revealed two strong obsessive factors as well as two strong
compulsive factors. Sanavio (1988) labeled the first obsessive factor ‘impaired control over mental activities’. This factor
was composed of items measuring an inability to stop unpleasant thoughts or ruminations (e.g. “Unpleasant thoughts come
into my mind against my will and I cannot get rid of them.“). The second obsessive factor, ‘urges and worries of loss of
control of motor behavior’, involved fears that impulsive thoughts of a violent or sexual nature would be manifest in action
(e.g. “I sometimes feel the need to break or damage things for no reason.“). The two compulsive factors, ‘becoming
contaminated’ and ‘checking behaviors’, were the two traditional ‘washing’ and ‘checking’ dimensions which prior research
has found in the CAC and MOCI (e.g. Sternberger & Burns. 1990). The PI aouears to hold oromise as an instrument which
will allow an expanded study of obs&ions and-compulsions in chnical and*nonclinical samples, particularly since it is the
only self-report measure which includes strong obsessional dimensions as distinct from compulsive dimensions.
Our purpose in this study was to continue the evaluation of this measure. Our goals were to provide the initial American
norms for the PI as well as to examine its psychometric properties. Specifically, we wanted to examine its internal
consistency, factor structure and convergent/divergent validity. Of primary interest was whether we would be able to
replicate the two obsessional and two checking factors with an American sample. For a test of convergent/divergent validity,
we selected the Symptom Checklist-90 Revised (Derogatis. 1983) and MOCI. It was expected that the Padua Inventory
would show a stronger correlation with the SCL-90-R obsessive-compulsive subscale than the other eight symptom
subscales (e.g. somatization, interpersonal sensitivity, depression, anxiety. hostility, phobic anxiety, paranoid ideation and
psychoticism). It was also expected that the corresponding subscales on the PI and MOCI would show a stronger correlation
than the noncorresponding subscales (i.e. washing with washing and checking with checking should correlate stronger than
washing with checking).

METHOD

The Ss were 701 Washington State University undergraduates enrolled in introductory psychology courses. Students who
did not speak English as a first language were not included in the analyses. This left a total of 678 Ss with a mean age

‘To whom all correspondence should be addressed

ssr ?8LF 341

342 CASE HISTORlES,4SD SHORTER COMMUSICATIONS

of 18.55 (Xl = 1.52).The sample of 678 Ss contained 354 females (5796) and 294 males. Ninety-one percent of the sampIe
was Caucasian.

Pa&n incenror~. The PI (Sanavio, 1988) is a @item self-report inventory which measures obsessions and compulsions.
Each item, rated on a j-point scale, measures the degree of disturbance caused by the thou&t or behavior (0 = ‘not at
al!’ and 4 = ‘very much’). The total score is the sum of the 60 items. The PI is considered to measure the extent to which
the obsessions and compulsions interfere with routine daily functioning. Table I shows the items on the PI.
Maudslev Obsessional-Cum~ulsive Inrenturv. The MOCI Wodnson. ”
& Rachman. 19771is a 30-item true-false self-rewrt
rm--
xate which measures OCD symptoms. A total score as well as washing (1 f items) and checking 19 items) subs&e scores
may be calculated for this questionnaire.
S+nprams Checklist-90 Rn:ised. The XL-90-R {Derogatis, 1983) is a 904em &f-report symptom inventory. Each item
is rated an a 5-point scale of distress from ‘not-at-all’ to ‘extremely’. The measure provides three total scores as well as
scores on nine symptom dimensions (obsessive-compulsive, depression, paranonid ideation, interpersonal sensitivity,
psychoticism, anxiety, somatization. hostility, and phobic anxiety).

Ss compieted the PI, MOCI. and the SCL-90-R in groups of 30-50, The admin~st~tion time was approx. 1hr. The Ss
were to!d that the purpose of the study was to find out how common the experiences listed on the questionnaires were
for college students.

RESULTS

The average item score on the PI was 0.69 with a range of 0.10 to 1.58. The internal consistency of the PI (coefficient
z) was 0.94. The average corrected item-total correlation was 0.45 (range 0.20 to 0.62) with the mean interitem correlation
being 0.21 (range -0.07 to 0.66). Only I9 of the IS00 interitem correlations were negative.
A principal components analysis with varimav rotation was also used to investigate the structure of the PI. A total of
I5 factors had eigenvalues > I. A plot of the eigenvalues (scree test) and the pattern of factor loadings suggested a
four-factor solution. Tabie I shows the factor loadings. Items were included on a factor if the loading was 0,40 or higher.
the same vatue used in Sanavio (19SS).
Factor 1, ‘impaired control of mental activities’. contained 20 items and explained 23.6% of the variance. This factor
inciuded such items as “I invent doubts and problems about most of the things I do” and “I find it difficult to make
decisions, even about unimportant matters”. The items which loaded on this factor replicated ail the items which loaded
on this factor in Sanavio (1985) except for item 34 (“Obscene or dirty words come into my mind and I cannot get rid of
them”) and item 38 (“When I hear about a disaster, I think it is somehow my fault”), which did not meet the O-40 criteria
in our study. Our results also had five additional items (L.7 13, 42, 45 and 48) which loaded on this factor.
The second factor. ‘checking’. contained 11 items, and explained 6.2% of the variance. Items such as “I tend to keep
on checking things more often than necessary” loaded on this factor. All the items which foaded on Sanauio’s (5988)
checking factor also Ioaded on our checking factor. We abo found three additional items (IS, 13 and I6) with Ioadings
>D.40 on this factor.
Factor 3. ‘urges and worries of losing control of motor behaviours’ (IO items), explained 4.3% of the variance. Items
such as ‘“I sometimes fee! a need to break or damage things for no reason ” loaded on this factor. The items which loaded
on this factor replicated the item loadings in the Sanavio (1988) study except that item 57 (“I fee! that I have to make special
gestures or walk in a certain way”) did not load ~0.40 in our study. In addition, we found four additional items (48%50,
52 and 56) with loading >0.40 on this factor.
The fourth factor. ‘being contaminated’. contained 10 items and explained 3.7% of the variance. This factor included
items such as “I avoid using public telephones because I am afraid of contagion or disease”. These IO items were the same
as found by Sanavio (l9SS). His eleventh item on this factor {No. 60) loaded 0.38 on this factor in our study. thus not
making the 0.40 criteria. The four factors together explained 37.8% of the variance with 41 of the 60 items on the PI loading
>0.40 on the four factors. Sanavio (1988) found 43 items with loadings >0.40. However, other than the few additional
items in our study with loadings 10.40, the results of our principal components analysis was very similar to his results.

Tote average ff score was 41.33 (SD = 25.11). There was no significant difference between female i;tl = 41.01, SD = 25.40)
and male (M = 42.08, SD = 26.27) means, 13676)= i I, NS. Our female mean, however, was significantly lower than the
16-20 and 21-25 female means in the Itaiian sample (Sanavio, 1988). r(442) = 23.23, P < 0.001 and l(468) = 5.58,
P < 0.001. In addition, our male mean was significantly lower than the mean for the 16-20-yr-old Italian males, but not
significantly different than the 21-25-yr-old Italian males, r(352) = 3.21, P < 0.01 and ((382) = 1.49. NS, respectively.
Strbscale scores
Subscale scores were calculated according to the recommendations of Sanavio (1988). The average score on his subscale 1
i If items). ‘imoaired contra! of mental activities’, was t 3.35 {SD = 9.5 1) (Cronbach’s z = 0.89. average corrected item-tota!
1

corre!ation r- 0.53. average interitem correlation = 0.32). The average score on the second subscaie f t t items), ‘becoming
contaminated‘. was 8.26 (SD = 5.66) (Cronbach’s II = 0.81, average corrected item-total correlation = 0.48, average
interitem correlation = 0.29). For the third subscale (8 items), ‘checking’, the mean score was 6.59 (SD = 5.61) (Cronbach’s
z = 0.87, average corrected item-total correlation =i 0.63, average interitem correlation - 0.47). There were no significant
differences between male and female scores on these three subscaies. The fourth subscale (7 items), ‘urges and worries of
losing contra! of motor behaviors’, had an average score of 3.00 (SD = 3.?6) (Cronbach’s LY= 0.37. average corrected
item-total correiation was 0.51. average interitem correhtion = 0.34). On this subscaIe the male (?A = 2.98, SD = 3.22) was
significantly higher than femaie mean {M = t.9#. SD = 2X4), r(676) = 4.60. P < 0.0001.
 CASE HISTORE AND SHORTER COMMUNICATIONS 343

Table 1. Factors and factor ioadinas for the Padua items

km Loading
Factor I: Impaired control of mental activiries
29 After’ doing something carefully. I still have the impression I have either done it badly or not finished it. 0.68
28 I have the impression that I will ncvcr be able to explain things clearly. especially when talking about important matters
that involve me. 0.68
31 I invent doubts and problems about most of the things I do. 0.65
33 Unpleasant thoughts come into my mind against my will and I cannot get rid of them. 0.64
26 I find it difficult to make decisions. even about unimportant matters. 0.61
27 Sometimes I am not sure I have done things which in fact I know I have done. 0.55
36 I imagine catastrophic conscqucnces as a result of absent-mindedness or minor error which I make. 0.55
35 My brain constantly goes its own way, and I find it difficult to attend to what is happening around me. 0.53
12 When I talk. I tend to repeat the same things and the same sentence several times. 0.53
45 in certain situations. I am afraid of losing my self-control and doing embarrassing things. 0.53
37 I think or worry at length about having hurt somconc without knowing it. 0.52
42 When 1 read I have the feeling I have missed something important and must go back and nrcad the passage at least
two or three times. OS0
32 When I start thinking of certain things I become obsessed with them. 0.50
59 When I hear about a suicide or crime, I am upset for a long time and find it difficult to stop thinking about it. 0.48
30 I am sometimes late because I keep doing certain things more often thnn necessary. 0.48
44 When a thought or doubt comes into my mind, I have to examine it from all points of view and cannot stop until I
have done so. 0.46
43 I worry about rcmcmbcring completely unimportant things and make an effort not to forget them. 0.45
58 In certain situations. I feel an impulse to cat too much.even if I am ill. 0.42
It When doubts and worries come to my mind. I cannot rest until I have talked them over with a reassuring person. 0.4 I
I3 I tend to ask people to repeat the same things to mc several times consecutively even though I did understand what they
said the first time. 0.40
20 I check and recheck gas and water tdps and light switches after turning them off. 0.71
22 I keep on checking forms, documents, checks, etc. in detail to make sure I have filled them in correctly. 0.69
21 I return home to check doors, windows, drawers, etc. to make sure they are properly shut. 0.68
23 1 keep on going back to see that matches, cigarettes, etc. arc properly extinguished. 0.67
25 I check letters carefuily many times before posting them. 0.65
19 I tend to keep on checking things more often than necessary. 0.64
24 When I handle money I count and recount it several times. 0.62
15 Before going to sleep I have to do certain things in a certain order. 0.47
16 Before going to bed, I have to hang up or fold my clothes in a special way. 0.47
18 I have to do things several times before I think they are properly done. 0.44
14 I feel obliged to follow a particular order in dressing. undressing. and washing myself. 0.40

Factor 3: Urges and worries of losing control of motor behavior

53 I sometimes t&l a need to break or damage things for no reason. 0.69
50 Seeing weapons excites me and makes me think of dangerous thoughts. 0.67
49 While driving. I sometimes feel an imputsc to drive the car into someone or something. 0.66
54 I sometimes have an impulse to steal other people’s belongings even if they are of no use to me. 0.62
56 I sometimes have an imp&c to hurt defenseless children or animals. 0.61
47 When I see a train approaching. I sometimes think I could throw myself under its wheels. 0.57
55 I am sometimes almost irresistibly tempted to steal something from the supermarket. 0.52
46 When I look down from a bridge or a very high window, 1 feel an impulse to throw myself into space. 0.52
48 At certain moments I am tempted co tear of my clothes in public. 0.48
52 I sometimes feet something inside me which makes mc do things which are really senseless and which I do not want to do. 0.47

Factor 4: Being contaminated

6 I avoid public telephones because I am afraid of contagion or disease. 0.66
5 I avoid using public toilets because I am afraid of disease and contamination. 0.63
4 I find it difficult to touch garbage or dirty things. 0.63
3 I find it difficult to touch an object when I know it has been touched by strangers or by certain people. 0.63
7 1 wash my hands more often and longer than necessary. 0.61
10 If an animal touchn me. I feel dirty and immediately have to wash myself or change my clothing. 0.59
9 If I touch something I think is ‘contaminatc~, I immediately have to wash or clean myself. 0.52
8 I sometimes have to wash or clean myself simply bccausc I think I may be dirty or contaminated. 0.51
2 I think even slight contact with bodily secretions (perspiration. saliva, urine, etc.) may contaminate my clothes or
somehow harm me. 0.50
I I feel my hands arc dirty when I touch money. ” d3

I, = 678.

Concergenr and divergent calidir)

Table 2 shows the correlations between the total score on the PI with each of the SCL-90-R subscales. The PI total score
correlated significantly with the SCL-90-R obsessive-compulsive (OBC) subscale, r(676) = 0.66. P < 0.001. In addition, this
correlation was significantly larger than correlation of the PI total score with the eight other SCL-90-R subscales
(P -C 0.001). The PI total score thus showed convergent and divergent validity with the SCL-90-R subscaIes.
Table 3 shows the correlations between the corresponding and noncorresponding subscales from the PI and MOCI.
The correlations between the corresponding subscales (checking with checking and washing with contamination) were
significantly larger than the noncorresponding subscales (P < 0.001). thus providing evidence for convergent and divergent
validity at a subscale level. Finally, the correlation was between PI and MOCI was significant, r(676) = 0.68, P c 0.001,
producing a value very similar to the r of 0.70 found by Sanavio in an Italian sample of college students.
 34 CASE HISTORIESAND SHORTER COMMUNKATIONS

Tjble 2. Padua Inventory (PI) total and subscale Table 3. Correlations between checkmg and washing subscales of PI
correlations uith the SCL-90-R subscales and MOCI
SCLR-90-R subscales PI-total Pi-contamination PI-checking
Obsessive-compulsive 0.66 %tOCIwashing 0.53 0.32
DepressiOn 0.5s MOCl checking 0.35 0.68
Interpersonal sensltwity 03
Paranoid ideation 033
n = 678. .MOCI= Maudsley Obsessional-Compulsive Inventory.
.&nGety 0.53
PI = Padua Inventory. Corresponding correlations are signifi-
cantly larger (P < 0.001) than noncorresponding correlations.
Ps>choticirm 0.52
Ail correlations significant at P < 0.0001.
Somatitalion 0.37
Hostility 0.44
Phobic anxietv 0.43
n =678. All correlations are significant at
P < 0.0001.

The present study investigated the psychometric properties of the Padua Inventory. a new measure of obsessive-
compulsive symptoms. This study also provided original normative data on a large. American nonclinical sample. This
information is important for establishing the outcome for clinical trials (Kendall & Grove, 1988) and as a standard of
comparison when studying OCD in nonclinical populations (Shet, Frost & Otto. 1983; Sher, Mann & Frost, 1984).
The results from this study are very similar to Sanavio’s (1988) for a large nonclinical Italina sample. Specifically. the
PI demonstrated good internal consistency in both studies. The factor structure in our American sample was simiiar to
the factor structure in the Italian sample. A four-factor solution most clearly fit the data. and explained 38% of the variance.
Each factor closely matched Sanavio’s factors with only a few exceptions in terms of specific items-2 items on the first
factor ‘impaired control of mental activities’, I item on the ‘urges and worries of losing control of motor behaviors’ factor,
and I item on the ‘being contaminated’ factor. The checking factor found in this study replicated exactly Sanavio’s checking
factor. The results provide evidence of the stability of the PI factor stucture in different populations as well as across cultures.
The results for the obsessional scales are particularly noteworthy. The two most widely used OCD measures. the CAC and
the ZVIOCI,measure primarily compulsive behavior (Freund ef al., 1987; Hodgson & Rachman, 1977). The PI is the first
OCD measure with two specific obsessional scales. Our results provide initial evidence that these obsessional factors emerge
across samples.
The mean total score on the Pi for females in our study was significantly lower than Sanavio’s female scores at ages
16-20 and 21-25. Males in our samples also scored significantly lower than the l6-20-yt-old Italian males. In addition,
Sanavio found females scored significantly higher than males on the total PI score while we failed to find a significant gender
difference. The causes and clinical significance of these differences are unknown at this time.
The four PI subscales also showed good internal consistency with z ranging from 0.77 to 0.89. A significant gender
difference emerged on onIy one of the subscaies-the ‘urges and worries of losing control of motor behaviors’ subscale.
Similarly, Sanavio reported males scored signi~cantly higher than females on the items measuring antisocial thoughts and
violent impulses (items 49, 54, 55 and 56). These four items all load on the ‘urges and worries of losing control of motor
behaviors’ subscale. Sanavio speculates that men may be more iikeiy to admit antisociaf behavior, or that this gender
difference represents actual differences in male and female beliefs and perceptions. It is unclear in our sample which
explanation may be more accurate.
The PI demonstrated good convergent and divergent validity with the SCL-90-R and MOCI. The PI total score correlated
significantly with the SCL-90-R obsessional scale, and this correlation was significantly different than the PI’s correlation
with any other SCL-90 subscale. In addition. the PI and MOCI corresponding subscales correlated with one another and
these correlations were significantly different than the correlations between noncorresponding subscales. Finally, the PI and
MOCI correlated 0.68, a value similar to the 0.70 correlation found by Sanavio. These results indicate that the PI correlates
well with other OCD measures, and diverges from other dissimilar symptom measures.
The present report provides evidence of the PI’s reliability and validity in a nonclinical sample. The PI thus appears to
be a promising instrument in assessing both obsessions and compulsions. The two studies to date, the first in Italy and
the second in the United States. produced very similar results and suggest that the PI may be a useful measure of OCD
phenomena. The PI, because of its unique obsessional scales, may be particularly useful in examining the obsessional
dimension of OCD. The PI may also be useful in facilitating the increasing amount of research on OCD phenomena in
nonclinical samples (Dent & Salkovskis, 1986: Frost, Sher 2%Green. 1986, Rachman & de Silva, 1978: Salkovskis Br
Harrison. 1984). particularly if the PI subscales prove useful in the testing of theoretical formulations of OCD (Salkovskis,
1989).

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