An RCT 1using a block design with allocation by area evaluated the effectiveness of a 12 week group based intervention, the Webster-Stratton Incredible Years basic parenting programme, as a preventive intervention with parents of preschool children considered to be at risk of developing conduct disorder. 153 parents from socially disadvantaged areas, with children aged 36-59 months at risk of conduct disorder defined by scoring over the clinical cut off on the Eyberg child behaviour inventory were randomised on a 2:1 basis, 104 to intervention and 49 to remaining on the wait listing (control). Twenty (13%) were lost to follow-up six months later, 18 from the intervention group. At follow-up, most of the measures of parenting and problem behaviour in children showed significant improvement in the intervention group. The intention to treat analysis for the primary outcome measure, the Eyberg child behaviour inventory, showed a mean difference between groups of 4.4 points (95% confidence interval 2.0 to 6.9, P<0.001) on the problem scale with an effect size of 0.63, and a mean difference of 25.1 (14.9 to 35.2, P<0.001) on the intensity scale with an effect size of 0.89.
A cost effectiveness analysis 2was performed alongside the pragmatic RCT. The bootstrapped incremental cost effectiveness ratio point estimate was 109 € per one point improvement on the intensity score. It would cost 8190 € to bring the child with the highest intensity score to below the clinical cut-off point and 2006 € to bring the average child in the intervention group within the non-clinical limits on the intensity score (below 127). For a ceiling ratio of 149 € per point increase in intensity score, there is an 83.9% chance of the intervention being cost effective. The mean cost per child attending the parenting group was 2887 € for eight children and 1924 € for 12 children, including initial costs and materials for training group leaders. When the sample was categorized into relatively mild, moderate, and severe behaviour groups based on intensity scores at baseline the intervention seemed more cost effective in those with the highest risk of developing conduct disorder.
Comment: The quality of evidence is downgraded by imprecise results (few patients).
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