Purpose
In this research, a disaggregate analysis of road accident injury under-reporting in selected European countries is presented.

Method
The level of injury under-reporting is expressed by under-reporting coefficients, estimated as the actual estimated number of road accident injuries of a given severity to the number of related injuries recorded by the Police. These coefficients were calculated within national/regional studies in the examined countries, through a specially developed uniform methodology of linking and matching Police road accident records and hospital records. Log-rate models are developed in order to estimate the combined effects of country (CZ, FR, GR, HU, NL, ES and the UK), road user type (car occupant, motorcyclist, pedal cyclist, pedestrian), Police severity score (serious or slight injury) and MAIS score (the maximum Abbreviated Injury Scale score) on under-reporting.

Results
The results suggest that the examined characteristics have important combined effect on under-reporting (i.e. third-order interaction). The results of the analysis of lower-order interactions reveal specific particularities of each country/region, indicating areas on which authorities should focus their efforts.

Conclusions
For example, it was found that slight injuries are more likely to be under-reported than serious injuries in the Czech Republic, France, and Greece, while the opposite is the case for the Netherlands and the UK. Moreover, although the Netherlands do not present high under-reporting rates overall, a particular issue is identified in this country for pedal cyclists’ slight injuries. Finally, a considerable part of total under-reporting in most countries can be attributed to injury severity mis-reporting.

Within this research, the police under-reporting of non-fatal road accident casualties in eight European countries was examined by means of a common methodology applied in each country. Eight national studies were carried out using the common methodology, and this allowed to prepare valid estimates of the level of under-reporting of non-fatal road casualties in Europe in a disaggregate form (namely by country, road user type and injury severity). This provided an insight into the variation of road casualty under-reporting in Europe. Moreover, a new common definition for road casualty severity was proposed that makes use of internationally recognised medical standards. This was established by examining two different injury severity standards, the casualty’s length of stay in hospital and the casualty’s maximum AIS score. The under-reporting coefficients developed within this research were applied to estimate the real number of non-fatal serious road accident casualties, according to the new proposed common definition. For almost all countries, the actual number of serious casualties according to the new proposed definition was found lower than the number of police-recorded serious casualties. With the newly estimated number of serious casualties, the values of the ratio of serious casualties to fatalities are much less widespread across countries. These remaining differences can thus be attributed to real differences in road safety between the countries, after having controlled for the different under-reporting levels and injury severity definitions.