Chronbach’s Alpha is a way to measure the internal consistency of a questionnaire or survey.
Cronbach’s Alpha ranges between 0 and 1, with higher values indicating that the survey or questionnaire is more reliable.
The easiest way to calculate Cronbach’s Alpha in SPSS is to use Analyze > Scale > Reliability Analysis.
The following example shows how to do so in practice.
Example: How to Calculate Cronbach’s Alpha in SPSS
Suppose a restaurant manager wants to measure overall satisfaction among customers.
She decides to send out a survey to 10 customers who can rate the restaurant on a scale of 1 to 3 for various categories.
The following dataset shows the ratings that each of the customers gave to the 3 questions on the survey:
To calculate Cronbach’s Alpha for the survey responses, click the Analyze tab, then click Scale, then click Reliability Analysis:
In the new window that appears, drag Q1, Q2 and Q3 into the Items panel.
Leave Alpha selected in the Model dropdown to indicate that you’d like to calculate Cronbach’s Alpha.
Next, click the Statistics button in the top right corner and then check the boxes under Descriptives for Item, Scale and Scale if item deleted:
Then click Continue. Then click OK.
The following output will be shown:
From the output we can see that Cronbach’s Alpha is 0.773.
The Item Statistics and Item-Total Statistics show various descriptive statistics for each individual question on the survey along with the value of Cronbach’s Alpha if individual items were deleted from the survey.
The following table describes how to interpret different values of Cronbach’s Alpha:
|0.9 ≤ α
|0.8 ≤ α < 0.9
|0.7 ≤ α < 0.8
|0.6 ≤ α < 0.7
|0.5 ≤ α < 0.6
|α < 0.5
Since we calculated Cronbach’s Alpha to be 0.773, we would say that the internal consistency of this survey is “Acceptable.”
Bonus: Feel free to use this Cronbach’s Alpha Calculator to find Cronbach’s Alpha for a given dataset.