Health impact assessments

There are two main dimensions along which public mental health can extend the reach of conventional psychiatry, given that mental illness and mental well-being seem coterminous, at least for common disorders. ^{Reference Huppert and So5} The first is to address population-level influences on well-being through policy advice, which may be evaluated by health impact assessments. Public Health England has been developing a methodology to include mental health – mental health impact assessments (MHIAs). There have been promising results, but the author lists of published MHIAs ⁶ suggest that psychiatrists are not typically engaged in their selection, design, deployment or feedback into policy. For example, Appendix 1 lists several individual and macro-economic factors affecting mental well-being, ^{Reference Rodríguez-Pose and Maslauskaite7} some of which might be adjusted by judicious policy choice.

Appendix 1 makes two key points: much policy affecting mental well-being involves sectors outside psychiatry; and excess, as well as inadequate expenditure may harm mental health. Part of public health involves achieving the most cost-effective deployment of available health interventions, which emphasises good health economics. Even with good economic measurement, difficulties may arise when, as is common in public health, a health-related intervention is not provided by a health-based organisation. Based on 2009 prices, social and emotional learning programmes in schools costs £132 per child, borne by education. After 10 years, total public savings resulting from improved behaviour are £10 164. However, the total savings to education after this time are £186, ^{Reference Knapp, McDaid and Parsonage8} so there is little incentive for education to further develop the programme, as costs are barely covered in its current form. Perverse incentives such as these may have contributed to the failure of significant public mental health interventions. MHIAs that include an economic component, promoted in government by appropriately qualified advisors, could recommend that those departments that obtain most economic benefit from interventions are the ones to pay for them, reducing such risks.

Logical framework matrix

The second dimension in public mental health – interventions across the whole population – is currently best discussed in children, where associations between population mean scores and prevalence have been published: for them, a 0.6 standard deviation reduction in population mean predicts a 1 unit decline in log-odds prevalence of psychiatric disorders. ^{Reference Huppert and So5} So, whole-population interventions with effect sizes too small for clinic use could still produce worthwhile reductions in population prevalence. For example, a randomised controlled trial of a whole-school intervention for aggressive behaviour estimated a parent-reported effect size of 0.26. ^{Reference Malti, Ribeaud and Eisner9} Assuming a population prevalence for behaviour disorders of 6.5% for boys ^{Reference Meltzer, Gatward, Goodman and Ford10} the intervention could reduce this prevalence to 4.3%, a reduction of nearly 34%.

Most psychiatrists practice without relevant local epidemiology, which public health calls ‘health intelligence’ and regards as essential for planning appropriate service delivery. Much can be extrapolated from national epidemiology and service activity data, but the impact of locally important changes (such as the loss of a major employer or service reconfiguration) on communities is not directly measured. The complex data-set linkages necessary to detect these routinely are still in development, ^{Reference Hollis, Martin, Amani, Cotton, Denis, Lewis and Davies11} so public mental health interventions, especially local ones, are currently difficult to evaluate. These evaluations are often of a different form to either conventional audit or research. Frequently, the intervention is well-understood, but the unknown is whether the intervention's environment will permit success, and how it might be favourably modified. A structure appropriate for these evaluations, the logical framework matrix, is shown at Appendix 2. Its cells are populated using the logical framework approach, ¹² which is commonly used in international health and development, but not taught in domestic mental health delivery or research.

Early intervention

Another subtle, but significant difference between public health and psychiatry is in the use of the term ‘early intervention’. In psychiatry, particularly in relation to psychosis, early intervention refers to intervention when at least some (psychotic) symptoms are present, but significant disability (or the full syndrome) has not yet had time to manifest. Public health would call this secondary prevention, reserving the first term for interventions occurring early in the natural history of the disorder. In public mental health, these would typically be primary prevention programmes, applied to young children. For example, interventions to reduce the prevalence and impact of early trauma might ameliorate the subsequent development of psychiatric disorders. ^{Reference Green, McLaughlin, Berglund, Gruber, Sampson and Zaslavsky13} In the UK, this distinction became practically important between 2005 and 2009, when there was both a 16.5% reduction in children aged 0–4 and an increase of 27% in in-patients aged 15+ being seen by Child and Adolescent Mental Health Services (CAMHS), based on (respectively) CAMHS mapping and hospital episode statistics, in the context of increasing concern about early intervention. The public health definition is harder for psychiatry to implement, as the very low base rates inevitably associated with these interventions make adequate effect sizes hard to demonstrate, and the relevant proxy for outcome may not be a psychiatric disorder at all. ^{Reference Hamre, Pianta, Mashburn and Downer14} Overall, however, the evidence overwhelmingly supports the value and cost-effectiveness of perinatal and preschool public mental health interventions, for physical as well as mental health difficulties, across the whole population. ^{Reference Foreman and Hulne-Dickens15} Therefore, interpretation of the government's focus on early intervention in psychiatric terms was associated with a reduction in the total amount of early intervention provided by psychiatry.