Although the quest for better measurement of individual job performance has generated considerable empirical research in industrial and organizational psychology, the feeling persists that a good job is not really being done in measuring job performance. This research project investigated the effects of differences in both individual and systems characteristics on the accuracy of job performance measurements using rating of individual effectiveness in fulfilling job duties. The research involved 4 studies over a period of 13 months. Subjects included 134 graduate students, 8 human resources managers, and 201 undergraduate students. Results indicate that: (1) the purpose for which performance ratings are collected does not affect accuracy; (2) the quality of the instructions that accompany the rating form can affect rating accuracy; and (3) the use of performance standards on the rating form and their effect on rating accuracy depend on the method used to collect the performance ratings. In addition, rater motivation, acceptance, and confidence are related to rating accuracy. The investigation of the methodologies used to collect the accuracy data suggests the need for new methods in future studies of rating accuracy. Eleven tables present study results, and 19 figures illustrate the discussion. Ten appendixes contain study questionnaires and instructions, and supplemental information about the studies. (Author/SLD)