Objectives Prevention Index (PI) is a practical measurement tool which is currently used in Germany to monitor prevention activities at workplaces. The 12-item scoring system has 3 subscales rating technical, organisational and personnel-related internal safety conditions of a company. Each item has a rating value from 1 - 9, with higher values indicating higher level of safety conditions. The reliability and validity of this instrument were evaluated in a survey in 128 companies in the German metal industry during the time between December 2011 and May 2012.
Methods The Inter-rater-reliability of this instrument was examined by 2 trained safety engineers of the German Social Accident Insurance. One engineer is responsible for safety consulting of the rated company while the other one is responsible for other firms and less informed about the conditions in the rated company. The agreement of double ratings was quantified by interclass correlation coefficient (ICC) and absolute agreement of the rating values.
Construct validity of the score was examined by principle component analysis (factor analysis) while content validity was evaluated by quantifying the association between PI-values and 5-years injury rates of the corresponding companies. Poisson regression analysis was performed to assess the association between PI-values and 5-years injury rates adjusted for company size and related industrial sectors.
Results Our analysis indicates a moderate to good inter-rater-reliability (ICC = 0.46 - 0.75) of PI-values with an absolute agreement between 72% and 81%. Factor analysis identified three component subscales which meet exactly the structural measure theory behind the score. The Poisson regression analysis demonstrates that higher technical and personnel safety conditions (PI-value ≥7) are associated with decreased injury rates, while less association was found between organisational conditions and injury rates.
Conclusions This analysis indicates that PI is a valid and reliable instrument which can be effectively used to monitor safety conditions at workplaces.