Estimating non-fatal road casualties in a large French county, using the capture–recapture method

IntroductionNon-fatal road casualties are under-reported, with official figures coming from the police. In the French Rhône county, a road trauma registry constitutes a second source of reporting but its completeness needs to be assessed. We also wish to estimate an incidence rate of non-fatal road casualties that is corrected for under-count.MethodsHaving two sources of reporting available, we can apply the capture–recapture method under certain conditions. To take into account different reporting probabilities among casualties, the capture–recapture analysis is stratified according to injury severity (New Injury Severity Score = NISS), road user type and human third party. To evaluate the sensitivity of the capture–recapture estimate on the number of matched casualties between the police file and the registry, three scenarios of record-linkage are considered.ResultsFor serious (NISS 9+) non-fatal road casualties, the police ascertainment rate is at most 57%, the registry ascertainment rate is at most 87%, and the aggregate ascertainment rate is at most 95%. The ascertainment-corrected incidence rate for serious (NISS 9+) non-fatal road casualties is at least 65 per 100,000.ConclusionThe degree of completeness of the registry for serious casualties is rather high, though not satisfactory.