Daniel Müller and Philipp Weinschenk

The tendency of supervisors to judge an employee as either good or bad and then to seek out evidence supporting that earlier established opinion is regarded as one of the major problems of performance appraisal. We investigate the implications of this rater bias in a dynamic moral hazard model with a wealth-constrained agent. Although rater bias weakens the agent’s incentives to exert effort in late periods, at the same time it strengthens implicit incentives in early periods. Under the optimal contract, as long as rater bias is not overly strong, its adverse effect on late-period incentives is fully offset by exploitation of stronger early-period incentives and thereby leaves the principal’s profits unchanged.