A survey is to be conducted among the alumni of an education

A survey is to be conducted among the alumni of an educational institution to obtain impressions of their experience when they were in school. A questionnaire has been prepared that asks for their response against questions on a scale of one to five. If the standard deviation of the scores from similar past surveys is 0.7, and the present results are desired within an error of ±0.2 with a 95% confidence level, how many alumni should be surveyed?

Solution

Compute Sample Size
n = (Z a/2 * S.D / ME ) ^2
Z/2 at 0.05% LOS is = 1.96 ( From Standard Normal Table )
Standard Deviation ( S.D) = 0.7
ME =0.2
n = ( 1.96*0.7/0.2) ^2
= (1.37/0.2 ) ^2
= 47.06 ~ 48