Sample size determination for observational studies

[MSchwartz]

Hi,

You might want to review the following two threads:

Sample size estimation

Hello, I want to design a registry study. However, the sample size will need multiple country registries as any one country will not have enough sample size. How do I determine the sample size for each country and when to stop so that the meta-analysis later will have enough power? If only study level data can be used for the meta-analysis, will that cause a problem? How do we convince the agency? Thank you so much! Kind regards, Huifang

and:

Power analysis in observational studies

Does anyone have a good reference about power analysis in observational studies, mostly retrospective ones? I have read conflicting opinions on this topic.

as they cover this topic and related issues.