Accuracy rates are improving. Current levels of reported accuracy suggest that routinely collected data are sufficiently robust to support their use for research and managerial decision-making.

The performance of a given comorbidity measure depends on the patient group and outcome. In general, the Elixhauser index seems the best so far, particularly for mortality beyond 30 days, although several newer, more inclusive measures are promising.

Objective To estimate the number of deaths and readmissions associated with delay in operation after femoral fracture. Design Analysis of inpatient hospital episode statistics. Setting NHS hospital trusts in England with at least 100 admissions for fractured neck of femur during the study period. Main outcome measuresIn hospital mortality and emergency readmission within 28 days. Results There were 129 522 admissions for fractured neck of femur in 151 trusts with 18 508 deaths in hospital (14.3%). Delay in operation was associated with an increased risk of death in hospital, which was reduced but persisted after adjustment for comorbidity. For all deaths in hospital, the odds ratio for more than one day's delay relative to one day or less was 1.27 (95% confidence interval 1.23 to 1.32) after adjustment for comorbidity. The proportion with more than two days' delay ranged from 1.1% to 62.4% between trusts. If death rates in patients with at most one day's delay had been repeated throughout all 151 trusts in this study, there would have been an average of 581 (478 to 683) fewer total deaths per year (9.4% of the total). There was little evidence of an association between delay and emergency readmission. Conclusions Delay in operation is associated with an increased risk of death but not readmission after a fractured neck of femur, even with adjustment for comorbidity, and there is wide variation between trusts.