# Simple size calculation in a X-sectional study - 95% CI, alpha 5%, existing prevalence 22%, response rate 80%, power (minimum) 80%

I would kindly need your support. I'm planning a research project to estimate the prevalence of hypertension (HTN) and diabetes mellitus (DM) in IDPs. The prevalence of HTN from other studies was 22% while that of DM was 10%. The total IDP population if of around 21,500, but if we include only those that respect the inclusion criteria, then the target population of the study is of around 13,500. Using the sample size formula n=Z2p(1-p)/d2 , where z-score = 1.96, p=0.22 (known prevalence of HTN) ,and d=0.05, I obtained n=264. Adjusting for a response rate of 80%, then n=264/0.8=330. I have two questions:

1. It is correct to take as reference the prevalence of HTN for the sample size calculation? Should I include also the prevalence of DM in the formula? And if yes, how can I do that?
2. Once obtained the sample size, and adjusted by the response rate, how can I check the power of my sample to make sure is at least 80% as the literature suggest?

I really appreciate your support. Alex