Correlation coefficients are the most popular statistical index in determining psychometric quality of physical activity (PA) measures or behaviors. The correlation coefficients describe the relationship between two variables. There are five major correlation coefficients, namely the Pearson product-moment correlation coefficient (PMM, r), Spearman’s Rho (rho), Phi coefficient, and Point-Biserial correlation coefficient and Biserial correlation coefficient. Among them, “PPM” (about 80%) and “rho” (about 20%) are usually used for physical activity research, according to a survey of recent published PA studies. The magnitude of PPM can be greatly affected by extreme values (outliers). To make outliers under control, we use rho in which we transform raw data into rank order. Statistically, PPM describes the correlation of the rank orders of two variables when outliers are included in raw data. Little guidance, however, is provided on when, why and how a correlation coefficient should be selected and applied. After a review of psychometric characteristics of these correlation coefficients, this presentation will provide a step-by-step tutorial on how to select appropriately a coefficient for a PA validation study. Some common mistakes in published studies will also be reviewed. Finally, examples on how to compute the coefficients using conventional statistical software will be illustrated.Keyword(s): . NA