Medical Sociology of Night-Shift Pharmacy Stock-Outs and Informal Drug Substitution in Tanzanian Mission Hospitals: A Diary-Study Estimation of After-Hours Scarcity Exposure

Night-shift pharmacy stock-outs in Tanzanian mission hospitals create a recurring dilemma: patients who present after hours may receive no drug at all, or may receive a substitute whose identity, dose and provenance are not recorded in any formal system. No observational data are used or claimed. Under a declared variance structure with between-cluster standard deviation of 6.0, residual standard deviation of 4.5 and intraclass correlation of 0.64, power was estimated across 2000 design cells spanning cluster counts of 8, 16, 24 and 32 and effect sizes of 3, 5 and 8 percentage points. The analysis indicates that 54 clusters are required to detect a 5-percentage-point effect at 80 per cent power. Informal substitution is not a residual category of pharmacy error but a structured social response to predictable temporal scarcity, and that diary-based estimation can render visible a form of exposure that routine health-management information systems are architecturally unable to capture.