Statistical modelling needed to find the effects from a community-based elderly safety promotion program.

BACKGROUND

Multiple control areas and time-series analyses have been recommended for effect evaluations of community-based health promotion. Large fluctuations, maybe due to chance, among the areas and over the years might obscure the intervention effect.

METHODS

A quasi-experimental time-series analysis with several control areas was performed as an effect evaluation of a community-based elderly safety promotion program. The program was implemented during 1995-99 in a community in the Stockholm Metropolitan area (population +65 years: 5500; number of first hip fractures in 1995: 60). Four control areas were selected based on similar hip fracture-related characteristics as the intervention community, complemented with two larger control areas. The time series covered 6 years pre-intervention (1990-95) and 6 years post-intervention (1996-2001). The study population was divided into two age groups and gender, resulting in 28 panels. The first hip fracture incidence was obtained from the Swedish national in-patient register.

RESULTS

The time series revealed no discernible pattern, and conventional analyses showed no conclusive results. A multivariate analysis, examining the time trends by employing the intra-annual and intra-panel variance, revealed the underlying trends in hip fracture rates. Comparisons between predicted numbers of hip fractures in the intervention and control areas was enabled, which resulted in 14 less hip fractures in the intervention community than expected from the control communities. If one extreme value was altered, the result changed considerably.

CONCLUSION

Effect evaluations of community-based health promotion programs using time-series from small communities might give faulty results, if statistical modelling is not employed.