Mp. Hagenzieker et al., EFFECTS OF INCENTIVE PROGRAMS TO STIMULATE SAFETY BELT USE - A METAANALYSIS, Accident analysis and prevention, 29(6), 1997, pp. 759-777
The effects of campaigns using tangible incentives (rewards) to promot
e safety belt usage have been evaluated by means of a meta-analytic ap
proach. Two coders extracted a total number of 136 short-term and 114
long-term effect sizes and coded many other variables from 34 journal
articles and research reports. The results show a mean short-term incr
ease in use rates of 20.6 percentage points; the mean long-term effect
was 13.7 percentage points. Large scale studies report smaller effect
sizes than small scale studies; when studies were weighted by the (es
timated) number of observations, the weighted mean effect sizes were 1
2.0 and 9.6 percentage points for the short and long term, respectivel
y. The main factors that influence the magnitude of the reported short
-term effect of the programs were the initial baseline rate (which was
highly correlated with the presence or absence of a safety belt usage
law), the type of population involved, whether incentives were delive
red immediately or delayed, and whether incentives were based on group
or individual behaviour. Together these four variables accounted for
64% of the variance. Other variables, such as the duration of the inte
rvention, the probability of receiving a reward, and the value of the
reward were not related to the short-term effect sizes. The relationsh
ip between moderating variables and long-term effects was less clear.
(C) 1997 Elsevier Science Ltd.