In this tutorial, we use correlation and simple linear regression to validate a selection tool -- or in other words, assess its criterion-related validity. First, we use the alpha function from the psych package to estimate the internal consistency reliability of a Conscientiousness personality scale to decide whether we should compute an overall scale score for all of the available items. Second, we use the Correlation function from the lessR package to estimate the validity coefficient for the conscientiousness scale in relation to job performance. Third, we use the Regression function from the lessR package to run a simple linear regression and to test the validity coefficient in an alternative manner. Finally, we discuss the concept of variance explained using the R-squared.