The Mid-Staffordshire Public Inquiry has published its findings. The initial investigations were triggered by an elevated hospital standardized mortality ratio (HSMR). This shows that the HSMR is being used as a screening test for substandard care; whereby hospitals that fail the test are scrutinized, whilst those that pass the test are not. But screening tests are often misunderstood and misused and so it is prudent to critically examine the HSMR before casting it in the role of a screening test for 'bad' hospitals. A screening test should be valid, have adequate performance characteristics and a clear post-test action plan. The HSMR is not a valid screening test (because the empirical relationship between clinically avoidable mortality and the HSMR is unknown). The HSMR has a poor performance profile (10 of 11 elevated HSMRs would be false alarms and 10 of 11 poorly performing hospitals would escape attention). Crucially, the aim of a post-test investigation into an elevated HSMR is unclear. The use of the HSMR as a screening test for clinically avoidable mortality and thereby substandard care, although well intentioned, is seriously flawed. The findings of the Mid-Staffordshire Public Inquiry have no bearing on this conclusion because a 'bad' hospital cannot uphold a bad screening test. Nonetheless, HSMRs continue to pose a grave public challenge to hospitals, whilst the unsatisfactory nature of the HSMR remains a largely unacknowledged and unchallenged private affair. This asymmetric relationship is inappropriate, unhelpful, costly and potentially harmful. The use of process measures remains a valid way to measure quality of care.