if all questions must have same manner same 5-point likert scale
if questions have different scales , SOME QUESTIONS have 2 points either yes or no . others are 5 point likert scale
second point related to number of respondents if ther minimal number
Hi, Wafaa,
Cronbach's alpha cannot be accurately calculated if the items are measured on different scales. You could convert the 5-point items to 2-point items, then calculate alpha, or you could calculate two different alphas - one for the 2-point items and one for the 5-point items.
There is no real minimum sample size required, but obviously, the larger the sample and the less variability in the responses will result in higher reliability results.
Dear Wafaa,
There are a lot of misconceptions about Cronbach's alpha. I recommend that you use a Principal Component Analysis instead.
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