To roughly estimate the sample size of a population needed to find a statistically significant correlation between two variables (assuming r values ranging from 0 to 1.0, α = [0.01; 0.05] and β = [0.05; 0.1; 0.2]), consider using Figure 13-7 from Norman & Streiner: Biostatistics: The Bare Essentials, 3rd edition, p 141, BC Decker […]