I want to study the differences between two groups: the treatment group and the comparison group. The total population consists of 60000 women in the treatment group, distributed across different states, cities, and districts. How should I select sample sizes from the same population to compare the two groups, and how many samples should I select to compare both groups??
The required sample for this population is about 382 people, but it can be increased to 450 people. Then the whole sample is divided into three different groups.
To determine sample size you need to specify the type of variable you are looking at, continuous or categorical, the degree of variability, the effect size you are looking for, and the statistical test you are using. The variability for a continuous variable is measured by the variance. For a binomial variable, which is categorical, it is calculated with a simple formula using the probability of the event, usually denoted “p”. A short explanation is given in, for example,
Calculating the Sample Size n: Continuous and Binary Random Variable,
https://openstax.org/books/introductory-business-statistics-2e/pages/8-4-calculating-the-sample-size-n-continuous-and-binary-random-variables
It is impossible to determine the appropriate sample size without estimates of the quantities mentioned above.
I agree with you, but my study will use quasi-experimental methods. How is the sample size for the two groups determined?
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