Cronbach's Alpha (α) using SPSS
Statistics
Introduction
Cronbach's alpha is the most common measure of internal consistency ("reliability"). It is
most commonly used when you have multiple Likert questions in a survey/questionnaire
that form a scale and you wish to determine if the scale is reliable. If you are concerned
with inter-rater reliability, we also have a guide on using Cohen's (κ) kappa that you
might find useful.
SPSS Statistics
Example
A researcher has devised a nine-question questionnaire to measure how safe people
feel at work at an industrial complex. Each question was a 5-point Likert item from
"strongly disagree" to "strongly agree". In order to understand whether the questions in
this questionnaire all reliably measure the same latent variable (feeling of safety) (so a
Likert scale could be constructed), a Cronbach's alpha was run on a sample size of 15
workers.
SPSS Statistics
Setup in SPSS Statistics
In SPSS Statistics, the nine questions have been labelled Qu1 through to Qu9 . To
know how to correctly enter your data into SPSS Statistics in order to run a Cronbach's
alpha test, see our guide: Entering Data into SPSS Statistics. Alternately, you can learn
about our enhanced data setup content on our Features: Data Setup page.
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SPSS Statistics
Test Procedure in SPSS Statistics
Cronbach's alpha can be carried out in SPSS Statistics using the Reliability
Analysis... procedure. In this section, we set out this 7-step procedure depending on
whether you have version 26 (or the subscription version) of SPSS
Statistics or version 25 or earlier. At the end of these seven steps, we show you how
to interpret the results from your Cronbach's alpha analysis.
Note: If you are unsure which version of SPSS Statistics you are using, see our
guide: Identifying your version of SPSS Statistics.
SPSS Statistics version 26
(and the subscription version of SPSS Statistics)
1. Click Analyze > Scale > Reliability Analysis... on the top menu, as
shown below:
Published with written permission from SPSS Statistics, IBM Corporation.
You will be presented with the following Reliability Analysis dialogue
box:
Published with written permission from SPSS Statistics, IBM Corporation.
2. Transfer the variables Qu1 to Qu9 into the Items: box. You can do this by
drag-and-dropping the variables into their respective boxes or by using
the button. You will be presented with the following screen:
Published with written permission from SPSS Statistics, IBM Corporation.
3. Leave the Model: option set as , which instructs SPSS
Statistics to run Cronbach's alpha.
Note: If you want to provide a name for the scale, enter it in the Scale label: box.
Since this only prints the name you enter at the top of the SPSS Statistics output,
it is certainly not essential that you do (in our example, we leave it blank).
4. Click on the button. You will be presented with the Reliability
Analysis: Statistics dialogue box, as shown below:
Published with written permission from SPSS Statistics, IBM Corporation.
5. Select the Item, Scale and Scale if item deleted options in the –Descriptives
for– area, and the Correlations option in the –Inter-Item– area, as shown
below:
Published with written permission from SPSS Statistics, IBM Corporation.
6. Click on the button. This will return you to the Reliability
Analysis dialogue box.
7. Click on the button to generate the output.
Now that you have run the Cronbach's alpha procedure, we show you how to interpret
your results in the Interpreting Results section. You can skip the section below, which
shows you how to carry out Cronbach's alpha when you have SPSS Statistics version
25 or earlier.
SPSS Statistics version 25 and earlier
1. Click Analyze > Scale > Reliability Analysis... on the top menu, as
shown below:
Published with written permission from SPSS Statistics, IBM Corporation.
You will be presented with the following Reliability Analysis dialogue
box:
Published with written permission from SPSS Statistics, IBM Corporation.
2. Transfer the variables Qu1 to Qu9 into the Items: box. You can do this by
drag-and-dropping the variables into their respective boxes or by using
the button. You will be presented with the following screen:
Published with written permission from SPSS Statistics, IBM Corporation.
3. Leave the Model: option set as , which instructs SPSS
Statistics to run Cronbach's alpha.
Note: If you want to provide a name for the scale, enter it in the Scale label: box.
Since this only prints the name you enter at the top of the SPSS Statistics output,
it is certainly not essential that you do (in our example, we leave it blank).
4. Click on the button. You will be presented with the Reliability
Analysis: Statistics dialogue box, as shown below:
Published with written permission from SPSS Statistics, IBM Corporation.
5. Select the Item, Scale and Scale if item deleted options in the –Descriptives
for– area, and the Correlations option in the –Inter-Item– area, as shown
below:
Published with written permission from SPSS Statistics, IBM Corporation.
6. Click on the button. This will return you to the Reliability
Analysis dialogue box.
7. Click on the button to generate the output.
