What is the minimun number of observations per answer that I need?

[Santiago Valdivieso]

I was running a regression and I obtained a very counter intuitive result (very high coefficient with statistical significance in the opposite direction of the expected one). When I looked for the possible causes, I realized that I had just 4 cases in one of the possible alternatives. My N=1200 and, following Cohen (1988), given my R2 and my number of regressors, my N should be of about 900 for a power and significance of .95. However, what happened to me with this 4 cases situation alerted me about this additional criteria that I should have in mind. What is the minimun number of observations per cases in each of the possible answers (for example, in a dummy variable)?

[Carlo Lazzaro]

Duplicate post. See replies at https://www.statalist.org/forums/for...r-a-regression.