Development of a psychometric measure of police driver risk
Collisions involving police vehicles or occurring as a result of police activity resulted in over 2000 casualties and 31 deaths in England and Wales in 2003-4. The assessment of police driver risk is currently restricted to subjective evaluations carried out by members of each force's police driver training team. Objective risk assessments are becoming increasingly popular with private companies operating fleets of vehicles, in an attempt to target training interventions at the drivers who are most at risk of collision involvement. This thesis reports the development of a psychometric measure of police driver risk using a series of qualitative and quantitative methods. The Driver Stress Inventory (DSI) was administered to 302 police drivers to establish its suitability as a basis on which to build the Police Driver Risk Index (PDRI). The Driver Stress Inventory is a well-established psychometric measure of driver stress, which consists of five behavioural factors and five coping factors. The DSI factor structure was largely replicated for the police sample. The generation of new police-specific items was facilitated by a series of in-depth semi- structured interviews with standard and advanced police drivers. The transcripts were analysed for common themes and items were generated from this analysis. The new PDRI was administered to a sample of 333 police drivers, and a Principal Components Analysis was carried out in order to establish the new factor structure and identify items contributing to the risk profile. Further refinement was carried out using an Item Discrimination Analysis, which allowed the length of the test to be reduced further. The effects of demographic and situational data on PDRI factor scores was investigated, and group differences were reported for age, sex, driving experience, and collision involvement. Test-retest reliability was investigated and a validation study using observational data, driver self-assessment and trainer assessment was carried out. The Police Driver Risk Index will be used to identify drivers at «highest risk of involvement in a collision, and pinpoint the areas in which they require remedial training. This will allow police forces to target their driver training resources more effectively.