# Standard deviation in SERVQUAL

I'm doing a project on measuring customer satisfaction using SERVQUAL. How do you calculate the standard deviation of each statement?

For example, if for one of the questions, there were:

• 2 respondents as strongly disagree (SD)
• 5 disagree (D)
• 20 neutral (N)
• 21 agree (A)
• 2 strongly agree (SA) (sample being 50)

How would you calculate the standard deviation if the scale were SD=1, D=2, N=3, A=4 and SA=5?

Also, how do you calculate the standard deviation for one dimension on the whole: e.g., the standard deviation for one of the dimensions in SERVQUAL say, Tangibles which has 4 statements or questions, and the standard deviation for Reliability which has 5 questions, etc.?

• Regarding your second point, if you have an estimate of scale reliability (test-retest measurement, or internal consistency--i.e., Cronbach's alpha), it can be used to compute the standard error of measurement of your scale scores. – chl Jul 17 '12 at 19:48