If organizations are to measure and use worker performance information effectively, they must distinguish between two components of performance appraisal: performance data (recorded information for comparing workers) and performance development (the process of improving human assets by discouraging ineffective and reinforcing effective job behaviors). Of the commonly used performance data types, unstructured and structured narratives suffer from a lack of common measures to compare workers as well as a high degree of rater subjectivity. Trait-defined scales offer structured measures but often have ambiguous dimensions and obscure methods for rating workers. Behaviorally anchored scales, developed to provide behaviorally specific definitions of dimensions and anchors, offer little advantage over trait-defined scales at considerable cost. End result data offer quantitative measures that reflect a worker's organizational contribution. If personnel development is a priority, however, a behavior observation scale (BOS) system may work best. A data and development system built around a BOS system can: (1) separate out the conflicting goals of clearly differentiating workers and insuring worker commitment to performance improvement; (2) create a data subsystem with steps to resolve conflicting views of performance levels; and (3) provide a development system that avoids direct comparisons and focuses on mutually acceptable, specific goal setting. (NRB)