AFTER DEFINING VALIDITY AND RELIABILITY, THREE BASIC TYPES OF VALIDITY-CRITERION, CONTENT, AND CONSTRUCT--ARE DISCUSSED. AN INTRODUCTORY DISCUSSION OF CLASSICAL TEST THEORY IS INCLUDED, WITH AN EMPHASIS ON PARALLEL MEASURES, FOLLOWED BY CONSIDERATION OF FOUR METHODS OF RELIABILITY ESTIMATION: TESTRETEST, ALTERNATIVE-FORM, SPLIT-HALF, AND INTERNAL CONSISTENCY. THE TEXT CONCLUDES WITH A DISCUSSION OF THE USE OF RELIABILITY ASSESSMENT FOR PURPOSES OF CORRECTING BIVARIATE CORRELATIONS FOR ATTENUATION DUE TO RANDOM MEASUREMENT ERROR. THE READER NEED BE FAMILIAR ONLY WITH SIMPLE CORRELATIONAL ANALYSIS IN ORDER TO FOLLOW THE PRESENTATION. FOR THE MORE ADVANCED READER, THE APPENDIX DISCUSSES THE USE OF FACTOR ANALYSIS IN RELIABILITY AND VALIDITY ASSESSMENT. BOTH THETA AND OMEGA RELIABILITY ESTIMATION ARE TREATED AND CONTRASTED WITH ONE ANOTHER AND WITH COEFFICIENT ALPHA, FOLLOWED BY A DISCUSSION OF THE ROLE OF FACTOR ANALYSIS IN EVALUATING THE VALIDITY OF A SET OF MEASURES. THE PRINCIPAL RECOMMENDATION IS THAT FACTOR ANALYSIS BE USED IN CONJUNCTION WITH THE METHOD OF CONSTRUCT VALIDATION IN ORDER TO ESTABLISH THE VALIDITY OF ANY SET OF MEASURES. (AUTHOR ABSTRACT MODIFIED)