Measuring Psychosocial Impact of CBRN Incidents by the Rasch Model.

An effective response to chemical, biological, radiological and nuclear (CBRN) incidents requires capability planning based upon an assessment of risks in which all types of possible consequences of such incidents have been taken into account. CBRN incidents can have a wide range of consequences of which psychological and social effects (possibly leading to societal unrest) are often pointed out as very likely to occur. The goal of our research was to establish an objective measurement of psychosocial impact of CBRN incidents with the use of the Rasch model. We created a list of eleven items, each of which tapped into an aspect of psychosocial impact of incidents. Eleven judges scored ten CBRN scenarios on this list of items. Two items needed to be removed due to misfit. The resulting nine-items test fitted the Rasch model well. Three items showed mild forms of differential item functioning, but were retained in the test. The reliability of the instrument was 0.83. The scale can be used to quantitatively measure the inherently qualitative nature of psychosocial impact of CBRN incident scenarios in order to better compare this type of impact with quantitative impact types such as number of casualties, costs, etc. Administration of the scale is simple and takes about one minute per scenario. We recommend wider use of the Rasch model for improving the quality of total impact measurement in case of being faced with both qualitative and quantitative types of impact.