Fig. 1

Mediation model illustrating all direct pathways and mediation pathways (dashed line). Abbreviations: AST, Active School Transport; PA, Physical Activity; T0, baseline; T1, 1-year follow-up; T2, 2-year follow-up. Path a, the effect of the AST at T0 (exposure) on PA at T1 (potential mediator), adjusted for T0 level of PA; Path b, the effect of PA at T1 on the outcome at T2, adjusted for level of the outcome at T1; Path c’, the direct effect of T0 AST on the outcome at T2, adjusted for T1 levels of both the outcome and PA