Sample size determination for observational studies

[R_cubed]

Check out section 5.6.5 in Frank’s Biostatistics for Biomedical Research (pdf) and use estimate precision instead. There are some references that will help justify a precision calculation when your audience is expecting power.

Also read the following thread for a rigorous observational study design:

RMS Causal Inference

Regression Modeling Strategies: Causal Inference and Directed Acyclic Graphics This is for questions and discussion about causal inference related to Regression Modeling Strategies. The purposes of these topics are to introduce key concepts in the chapter and to provide a place for questions, answers, and discussion around the topics presented by Drew Levy. RMScausal