Thirteen hospitals in Utah and 15 in Colorado participated in the study. Nurses reviewed 4943 (98.9%) of the 5000 sampled records in Utah and 9757 (97.6%) of the 10
000 records sampled in Colorado, representing 2.6% of all discharges in these states in 1992. Of these records, the nurses referred 854 (17.3%) Utah records and 2014 (20.6%) Colorado records to physicians for further review. The physicians reviewed 842 (98.6%) of the referred Utah records and 1978 (98.2%) of the referred Colorado records. The rest were classified as missing.
The demographic characteristics of the patients whose records were sampled were similar to the characteristics of all patients discharged in each state in 1992.4
Table shows that the reviewers detected 241 adverse events (of which 132 were preventable) among non-elderly patients (aged 16-64 years) and 207 adverse events (of which 117 were preventable) among elderly patients (aged ≥65). When these results were extrapolated to represent all discharges in each state in 1992, there were 8901 adverse events among non-elderly patients (incidence 2.80% (SE 0.18%)) compared with 7419 (5.29% (0.37%)) among elderly patients (P=0.001). For preventable adverse events, the incidence was also nearly twice as high in elderly patients: non-elderly patients had 5038 preventable adverse events (incidence 1.58% (SE 0.14%)) compared with 4134 (2.95% (0.28%)) in elderly patients (P=0.001).
Number and incidence of adverse events and preventable adverse events among patients discharged from hospitals in Utah and Colorado in 1992 by age group
A greater proportion of the elderly patients who experienced preventable adverse events had permanent disability or death as a result than did the non-elderly patients (8.66% (SE 2.75%) v 5.80% (2.11%) for permanent disability and 10.44% (2.96%) v 4.65% (1.94%) for death). However, these differences were not statistically significant (table ).
Disability and death due to preventable adverse events among patients discharged from hospitals in Utah and Colorado in 1992 by age group*
The elderly patients had a higher incidence of several types of preventable adverse events (table ). The incidence was significantly higher for preventable events related to medical procedure (such as thoracentesis or cardiac catheterisation) (0.69% (SE 0.14%) in elderly patients v 0.13% (0.04%) in non-elderly patients), preventable adverse drug events (0.63% (0.14%) v 0.17% (0.05%)), and preventable falls (0.10% (0.06%) v 0.01% (0.02%)).
Number and incidence of preventable adverse events among patients discharged from hospitals in Utah and Colorado in 1992 by type of event and age group*
After adjusting for the patient and hospital characteristics mentioned above, we found that age was not independently associated with preventable adverse events. The only patient characteristic associated with preventable adverse events was diagnosis related group (DRG) level. Compared with patients with DRG level 1 (the least complex DRG), patients with DRG level 2 had an odds ratio of 7.8 (P=0.001), patients with DRG level 3 had an odds ratio of 11.4 (P=0.0001), and patients with DRG level 4 had an odds ratio of 14.3 (P=0.0001) for suffering a preventable adverse event. Since DRGs are assigned to admissions retrospectively, a higher DRG level may indicate the presence of an adverse event during the admission in addition to, or instead of, more complex care. Therefore, we ran the model without the DRG level variable and found that age was still not independently associated with preventable adverse events.