different samples of respondents from the population complete the survey over a time period
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z test
The samples must be randomly selected, independent, and normally distributed. The following are necessary to use a t-test for small independent samples. 1. The samples must be randomly selected. 2. The samples must be independent. 3. Each population must have a normal distribution.
If the two samples are of size n1 and n2 then the t-statistic is distributed with n1 + n2 - 2 degree of freedom.
It is used when repeated trials are carried out , in which there are only two outcomes (success and failure) and the probability of success is a constant and is independent of the outcomes in other trials.
ome suggested ways: Larger samples, Better sample design, Better measurement, Better data validation, Better survey/questionnaire design.