Eighty-eight controlled studies (106,243 participants) were included in the review and 119 effect sizes were reported.
Overall there was a significantly greater effect for tailored interventions compared to control groups (fixed effect g=0.17, 95% CI 0.14 to 0.19 and random effect g=0.17, 95% CI 0.14 to 0.20; 88 studies). There was evidence of significant statistical heterogeneity (p<0.001).
All health behaviours reported significantly greater effects (fixed-effect) for tailored interventions compared to control groups for smoking cessation (g=0.16, 95% CI 0.12 to 0.19; 32 interventions), dietary fat reductions (g=0.22, 95% CI 0.18 to 0.26; 26 interventions), fruit and vegetable intake (g=0.16, 95% CI 0.10 to 0.21; 25 interventions), mammography (g=0.13, 95% CI 0.08 to 0.18; 12 interventions) and physical activity (g=0.16, 95% CI 0.10 to 0.21; 25 interventions).
Longitudinal analysis reported that although effects declined over time, results remained statistically significant for long-term follow-up (g=0.12, 95% CI 0.08 to 0.16).
Moderator analysis reported that effect size increased for every additional contact and dynamic tailoring was associated with larger effect sizes than static tailoring. Effect sizes increased across studies that intervened on one, two and three behaviours, but this trend did not continue with studies that intervened on four behaviours. No other moderator variables reported any significant differences. Orwin's fail-safe N showed that an additional 58 studies with null effects would be needed to reduce the overall effect size to a clinically non-significant outcome (g=0.10).