Perceived case complexity. Each pathologist rated each case for "Complexity". Complexity involved aspects of diagnostic difficulty, case management (i.e. the need for recuts or special stains), and reporting issues (i.e. the need for a diagnostic comment). The study appeared to include a balanced set of cases with "high", "medium", and "low" complexity.
Gilbertson et al. BMC Clinical Pathology 2006 6:4 doi:10.1186/1472-6890-6-4