The “black cloud” on call: a field study of cognitive bias in workload perception among physicians

The “black cloud” phenomenon, the belief that certain physicians disproportionately experience higher workloads during on-call shifts, is a recurrent anecdote in medical communities worldwide. However, it remains unclear whether this phenomenon reflects actual differences in workload or is a subjective belief. This study aimed to verify the objective basis of the “black cloud” perception and to interpret the observed phenomenon through a theoretical framework of cognitive psychology by analyzing on-call data from physicians working in the same clinical environment. A retrospective single-center observational study was conducted on four urologists (fellows) participating in the rotating on-call schedule at a tertiary teaching hospital in Seoul from March 2024 to June 2025 (15 months). The “black cloud” perception was defined not by surveys but by behavioral indicators, specifically persistent and vocal complaints regarding workload disproportion. All shifts (n = 493) were standardized to 12-hour units. The primary outcome was the number of emergency calls per shift. Secondary outcomes included the frequency of early morning calls (00:00–05:30) and high-call shifts (≥ 5 calls). Statistical analyses included descriptive statistics, one-way analysis of variance (ANOVA), negative binomial regression, and sensitivity analysis. A total of 493 on-call shifts were analyzed. There was no statistically significant difference in the mean number of calls per shift among the four physicians (1.25 vs. 1.12 vs. 1.21 vs. 1.22; F = 0.228, p = 0.877). The negative binomial regression analysis also confirmed no significant differences in the incidence rate of calls among individuals. Notably, the call frequency for Dr. Kim, who consistently expressed complaints, was numerically only slightly higher; however, this remained within the range of random variation and was not statistically significant. This study found no statistically significant differences in actual on-call workloads among urology specialists working in a shared environment. The discrepancy between self-perceived “black cloud” status and objectively measured workload suggests that this phenomenon may be better understood as a cognitive interpretation of experience rather than a statistically demonstrable workload imbalance.