Abstract.Variation in service quality results in service failure and subsequent customer defection, and thus knowing how to manage such variation is critical for service managers. However, little is known about why, and at which workplaces, some service employees can provide service of a consistently high quality but others cannot. This study addresses this issue using the perspective of signal detection theory. Multiplesource and matched data from 160 nurses and 480 patients were used for the analysis. We found that job tenure was negatively related to variation in all dimensions of service quality. Moreover, control over practice interacts with job tenure and expertise to impact service variation and the average level of all dimensions of service quality. These factors interactively determine whether service employees can provide a consistently high quality of service. To our knowledge, this is the first empirical study addressing this issue by examining viable employee and workplace characteristics. The findings provide a means for service managers to ensure a consistently high level of service quality.