Deliverable D 1.3 RESULTS OF META-ANALYSIS ... - cast-eu.org

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Campaigns and awareness raising strategies in traffic safety — Deliverable D-1.1campaigns of the future. Most of the effects given in this report weregenerated using a random effects model after accounting for publication bias.Table 7.19 Four possible estimates of the overall campaign effect on accidents. Each overalleffect is based on n individual effects (excluding any artificial effects generated by trim-andfill).OutcomemeasureModelAccount forpublicationbias?effect(%)95%confidenceintervalSignificant?(p < 0.05)fixed effects no - 10 (- 11 -10) yesaccidents(n = 118)random effects- 13 (-16; -9) yesfixed effect yes, generate -7 (- 8, -6) Yes26 effects torandom effects compensate -6 (-10;-1) yes7.3.1 SUMMARYAn example of the use of meta-analysis to generate en estimate of the overalleffects of campaigns on road accidents is given. An effect is a change inaccident counts (or percentage behaviour) occurring before and during / aftera campaign. Each effect is expressed as an odds ratio from which the naturallogarithm (ln) is taken. The ln odds ratio is then weighted according to thenumber of people or counts observed in the study. Individual weighted ln oddsratios are then summed and the sum divided by the sum of individual weightsto give an overall effect. The population of effects is checked for publicationbias and homogeneity in order to ensure that the overall effect is notoverestimated.70
Campaigns and awareness raising strategies in traffic safety — Deliverable D-1.17.4 OVERALL EFFECT OF CAMPAIGNSThe meta-analysis procedure described in section 7.3 was used to deriveconservative estimates of overall campaign effects for each of the outcomemeasures listed in Table 7.2 for which there were at least five individualeffects. The results are shown in Table 7.20.As reported in section 7.3, according to our sample road safety campaignsresult in an overall significant reduction in accidents of 6 per cent. Campaignsevaluated in the sample also produced favourable overall changes in roaduser behaviour, according to several different measures (Table 7.20). Wecalculated a substantial overall increase of 25 per cent in the use of seatbelts,a decrease of 16 per cent and 17 per cent, respectively, in speeding anddrink-driving behaviour and an increase in 37 per cent of drivers yielding topedestrians. Apart from the drink-driving result, each of these results wasstatistically significant.There were also favourable overall outcomes on some non-behaviouralmeasures. Not surprisingly, campaigns resulted in an overall substantial, ifsomewhat variable, increase (120 per cent) in the recall of the campaign, butthey also had a significant ability to increase understanding of risk (16 percent). The effect of road safety campaigns on attitudes was low and nonsignificant,and the effect on relevant road safety knowledge inconsistent.The original studies from which these overall effects are derived are given inAppendix B.Table 7.20. Overall effect of road safety campaigns on different outcome measures, afteraccounting for publication bias. Each overall effect is based on n individual effects.Outcome measureeffect(%)95%confidenceinterval (%)Significant?(p < 0.05)Number of accidents (n = 115) - 6 (-10, -1) yes% using seatbelts (n = 133) +25 (+18, +31) yes% speeding (n = 28) -16 (- 25, -6) yes% drink-driving (n = 23) - 17 (- 46, +28) no% yielding to pedestrians (n = 13) +37 (+14, +65) yes% expressing favourable attitude (n = 39) +5 (-0, +11) no% risk comprehension (n = 24) +16 (+4, +30) yes% correct knowledge (n = 17) +44 (-10, +132) no% recalling campaign (n = 23) +120 (+30, +273) yes71
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