CRONBACH’S ALPHA TEST
Reliability refers to the consistency of the results. A questionnaire used on a similar population that produces similar results can be termed as reliable. Cronbach’s alpha is the most common measure of reliability. It is commonly used when we have multiple Likert questions in a survey/questionnaire that form a scale and we wish to determine if the scale is reliable.
A researcher has devised a questionnaire with 4 questions named as v1, v2, v3, v4 to measure a particular variable. Each question is measurable on a 5-point Likert item from “strongly disagree” to “strongly agree”. A Cronbach’s alpha is run on a sample size of 20 items to understand whether the questions in this questionnaire (table-1) reliably measure the variable.
Table-1: Likert scale data in Questionnaire
Performing the Analysis with SPSS
For SPSS Version 11, click on Analyze ⇒ Scale ⇒ Reliability Analysis. This will bring up the SPSS screen dialogue box as shown below.
After clicking Reliability Analysis, this will bring up the following SPSS screen dialogue box
Select the variables and click them to move to Items box. Click Statistics and it opens up the following dialogue box.
Select Scale and Scale if item deleted under ‘Descriptive for’ and Correlations under ‘Summaries’ and then click Continue. This will bring up the following dialogue box.
Finally click OK to get the output.