Assessment centers (ACs) usually consist of several job-related exercises that tap competencies necessary for the job. ACs are most often used by organizations to select, promote, and develop their employees. Like many employee selection and assessment methods (e.g., interviews), ACs require a scorer or assessor to provide an evaluation of candidates’ performance.
THE RESEARCH STUDY
In two studies, the researchers (Melchers et al., 2010) found that assessor ratings of candidates decrease in accuracy as the number of candidates they assess simultaneously increases. While this finding may seem like a “no-brainer,” meta-analytic research (Woehr & Authur, 2003) has demonstrated that ACs with higher candidate-to-assessor ratios (i.e. fewer assessors evaluating more candidates) tend to be more valid than ACs with lower candidate-to-assessor ratios. However, as the authors of this study point out, the candidate-to-assessor ratio in an AC is not the concern here, its how many candidates an assessor must observe and evaluate simultaneously that apparently decreases rating accuracy.
As the authors note, experienced assessors may be able to assess two or three candidates on several competencies simultaneously while less experienced assessors may not. The key here is that AC designers should be aware that too high of a work load can negatively influence the accuracy of assessor ratings. Thus, when possible, the number of candidates an assessor is assigned to observe and evaluate simultaneously should be limited. Unfortunately, the authors do not provide exact recommendations for the ideal number of candidates that assessors should be assigned to assess simultaneously in an AC exercise.
THE BOTTOM LINE
This article makes the case for decreasing the workloads of assessors. Still, organizations may be concerned that increasing the number of assessors will cost more money. But ultimately, the initial costs associated with this approach will likely pale in comparison to the potential costs of hiring or promoting the wrong candidates.
Melchers, K.G., Kleinmann, M., & Prinz, M.A. (2010). Do assessors have too much on their plates? The effects of simultaneously rating multiple assessment center candidates on rating quality. International Journal of Selection and Assessment, 18(3), 329-341.