Population-level effectiveness of alternative approaches to preventing mental disorders in adolescents and young adults

Abstract

Preventive interventions that are effective in reducing the incidence of mental disorders in adolescence and early adulthood may impact substantially on lifetime economic, educational, and health outcomes; however, relatively few studies have examined the capacity of alternative approaches to preventing youth mental disorders (specifically, universal, selective, and indicated prevention) to reduce disorder incidence at a population level. Using a dynamic model of the onset of non-specific, relatively mild symptoms and progression to more severe disease, we show that: (1) indicated preventive interventions, targeting adolescents and young adults experiencing subthreshold symptoms, may often be more effective in reducing mental disorder prevalence than universal interventions delivered to the general population (contrary to the widely accepted view that a 'high risk' prevention strategy, focussing on those individuals with the greatest risk of developing a disorder, will generally be less effective than a whole-population strategy); and (2) the ability of selective preventive interventions (targeting vulnerable, asymptomatic youth) to alter the prevalence of mental disorders is severely restricted by an inverse relationship between the prevalence of significant risk factors for mental illness and the relative risk of developing symptoms.

Figure 1

Dynamic model used for the analysis. Notation is defined in the Results section and Table 1. Stocks (or compartments, state variables) are shown as boxes, flows as pipes with taps, causal connections (or mathematical dependencies) as arrows, and sources and sinks as clouds (see refs., ). Symbols with dashed outlines are copies (or ‘ghosts’) of the corresponding symbols with solid outlines.

Figure 2

Effectiveness of selective preventive interventions and empirical estimates of $\varphi$ and $\theta$. (A) Prevalence of full-threshold mental disorders under scenarios in which a selective intervention that halves the proportion of vulnerable adolescents and young adults at increased risk of developing symptoms ($h$ equal to 0.5) is introduced at time $t$ = 10³ and remains in place indefinitely. Results are presented for three sets of values for $\varphi$ and $\theta$. (B–C) Post-intervention equilibrium prevalence of full-threshold mental disorders as a function of the parameters $\varphi$ and $\theta$ (i.e., the proportion of adolescents turning 12 years exposed to one or more risk factors for mental illness and the relative risk of symptom onset, respectively). Dark red shading in panel B corresponds to higher equilibrium prevalence, pale yellow shading to lower equilibrium prevalence. In all cases, the equilibrium prevalence of full-threshold disorders is calculated assuming a value of 0.5 for $h$ (see Results section for further details). (D) Empirical estimates of $\varphi$ and $\theta$ for a diverse selection of risk factors (see Supplementary Table S1 for details).

Figure 3

Population-level effectiveness of universal, selective, and indicated preventive interventions for youth mental disorders. Each panel presents the post-intervention equilibrium prevalence of full-threshold disorders for universal (grey), selective (blue), and indicated (red) preventive interventions with varying individual-level effects ($-\mathrm{\Delta }u/u_0$, $-\mathrm{\Delta }h$, and $-\mathrm{\Delta }i/i_0$, respectively; see Results section for further details). Note that the population-level effectiveness of a selective preventive intervention is strongly dependent upon the parameters $\varphi$ and $\theta$ (i.e., the proportion of adolescents turning 12 years exposed to one or more risk factors for mental illness and the relative risk of developing subthreshold symptoms, respectively), as well as the individual-level intervention effect $-\mathrm{\Delta }h$.