Cronbach’s Alpha (α) Reliability Analysis using SPSS

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.


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.


Cronbach’s Alpha (α) Reliability Analysis Procedure

The eight steps below show you how to check for internal consistency using Cronbach’s alpha in SPSS Statistics. At the end of these eight steps, we show you how to interpret the results from your Cronbach’s alpha.

  1. Click Analyze > Scale > Reliability Analysis… on the top menu, as shown below:

    Cronbach's Alpha Test MenuPublished with written permission from SPSS Statistics, IBM Corporation.

  2. You will be presented with the Reliability Analysis dialogue box, as shown below:

    Cronbach's Alpha Dialogue BoxPublished with written permission from SPSS Statistics, IBM Corporation.

  3. 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 SPSS Right Arrow Button button. You will be presented with the following screen:

    Cronbach's Alpha Dialogue BoxPublished with written permission from SPSS Statistics, IBM Corporation.

  4. Leave the Model: set as “Alpha”, which represents Cronbach’s alpha in SPSS Statistics. 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).
  5. Click on the SPSS Statistics Button button, which will open the Reliability Analysis: Statistics dialogue box, as shown below:

    Cronbach's Alpha Dialogue BoxPublished with written permission from SPSS Statistics, IBM Corporation.

  6. Select the ItemScale and Scale if item deleted options in the –Descriptives for– area, and the Correlations option in the –Inter-Item– area, as shown below:

    Cronbach's Alpha Dialogue BoxPublished with written permission from SPSS Statistics, IBM Corporation.

  7. Click the SPSS Continue Button button. This will return you to the Reliability Analysis dialogue box.
  8. Click the SPSS OK Button button to generate the output.

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