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Campaigns and awareness raising strategies in traffic safety — Deliverable D-1.1significant in this final model and it explains only 2 per cent of the variance incampaign effects. A drink-drive theme was beneficial in terms of accidentreduction, alone explaining 6 per cent of campaign effect variance, and thebeneficial effect of enforcement on accidents was close to significance in themodel, where it explained 3 per cent of campaign effect variance. Finally,short campaign duration was beneficial (3 per cent of variance explained) andrecent campaigns (carried out after 2000) were associated with detrimentaleffects (12 per cent variance explained). The final model can be summarizedthus:Figure 8.1 Final model of relative influence of campaign factors on reducing accident counts.Factors in parentheses are included even though they do not appear to be significant accordingto the model, because they approach significance, have theoretical grounds to be included andwere found to be significant in a previous meta-regression analysis (Vaa et al., 2004).+_• drink-drive theme• short campaign duration• on-road delivery• (personal influence)• (enforcement)• recent campaigns, since 2000• use of combined mass-media8.2.1 CHECKS ON THE FINAL ACCIDENT MODEL1. Checks were made for collinearity and outliers. There were five outliers(maximum Mahalanobis distance = 54), but these were not omitted sincestatistical tests (maximum Cook’s Distance = 0.44) and trial exclusion ofaffected cases from the model indicated that they did not influence the finalmodel description unduly. It was assumed that homoscedasticity wasminimised by weighting the regression by the fixed effects weights.2. The variable [stripped mass-media] was created to identify those studyeffects associated with campaigns using at least one of the mediatelevision, radio or newspaper and no other delivery channel. Whereascombined mass-media -- which scored effects for campaigns usingtelevision and radio and newspaper with or without other channels -- canbe considered as representing ‘mass delivery’ campaigns, stripped massmediacan be considered as a test for those campaigns using only a singlemass media channel. A model was tested in which [stripped mass-media]was used in place of [combined mass-media]. Whereas the statistics forthe other six variables were very similar, [stripped mass-media] was notsignificant, indicating that a single mass-media channel is neitherbeneficial nor detrimental to campaign effects on accidents.3. Initially a decision was made to exclude country variables because wewere not sure what it would tell us about campaign effects. We wished104
Campaigns and awareness raising strategies in traffic safety — Deliverable D-1.1rather to identify what caused the variance between countries that wasresponsible for variance in campaigns effects. From the subgroupanalyses country was dummy coded as [USA] and [Australia]. In neithercase were there significant contributions from the country variables, eitherwhen they were added together or alone as variables to supplement thefinal model. Use of [Australia] improved the overall model slightly and itsinclusion increased the contribution and significance of the [personal]variable (beta = -0.17; p = 0.046).4. In CAST we made a decision to use effects reported by both controlledand non-controlled studies, and exclude non-controlled studies only if asa group they were significantly different from controlled effects. Subgroupanalyses suggested that the two groups were not significantly different.This enabled us to include more effects in meta-regression analyses, andthereby include more explanatory variables in the final model. To furthertest differences between effects from controlled and non-controlledstudies, two further checks were made in meta-regression: (a) [control]was added as a variable to the final model; and (b) the final model wasused to test those effects arising from controlled studies alone.a. A standard multiple regression was performed using [control] as asupplementary variable to the final model variables. The final modelvariables had the same properties as in Table 8.2, in terms ofdirection and significance of variable associations, and [control] wasnot significantly associated with the outcome variable (beta = -0.07;p = 0.48).b. A weighted standard multiple regression was performed using thefinal model variables on only controlled cases (n = 84). The analysisoutput results similar to those output for pooled controlled and noncontrolledcases (n = 112). Although significance of someassociations was lost, it was for the four weaker variables. Thiscould be expected from the reduced power resulting from thereduction in case number. The direction of all relationships with theoutcome variable remained the same. This gave us confidence thatthe use of a control group did not affect the qualitative conclusionsdrawn in Figure 8.1.5. A split-half analysis of the dataset was attempted based on whether thestudy came before or after 1993 (chosen because it gives a roughly 50:50split in study number). This was done to address concerns about therelevance of the final model to contemporary campaigns. There werefew significant relationships in either the pre-1993 or post-1993 outputmodel, but there are probably too few effects present in each half toenable conclusions to be made about this.8.2.2 SUMMARY OF FACTORS INFLUENCING CAMPAIGN EFFECTS ONACCIDENTSDuring model development some important variables had to be excluded,ultimately because there was not enough information about the campaigns inthe study evaluations. This prevented us from examining the way potentially105
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