Mental health is increasingly being recognised as a public priority in today’s societies and economies. Understanding and mapping both its positive and negative dimensions is key to informing a number of public policies and actions by the private sector and civil society. This report aims to support national statistical offices and other data producers in collecting high-quality measures of population mental health outcomes in a more frequent, consistent and internationally harmonised manner. It documents existing measurement practice across OECD countries, discusses the advantages and limitations of available measurement tools, and recommends priority measures (for both mental ill-health and positive mental states) to adopt in household, social and health surveys. While this report does not present fully-fledged measurement guidelines, it complements past OECD WISE Centre work aiming to advance the statistical agenda on people’s well-being, including guidelines on subjective well-being; trust; and the quality of the working environment. This publication is the first of two reports prepared as part of a special assessment of mental health and well-being in the context of the OECD How’s Life? publication series. The second report applies a well-being lens to population mental health by examining its interlinkages with the different economic, social, environmental and relational dimensions of people’s lives as exemplified by the OECD Well-being Framework.

Mental health plays a central role in people’s lives and is intrinsically tied to many other aspects of people’s wider well-being. This was underscored during the COVID-19 pandemic, when direct health impacts and loss of lives combined with social isolation, loss of work and financial insecurity all contributed to a significant worsening of people’s mental health. Data from 15 OECD countries suggest that by late 2020, over one-quarter of people experienced symptoms of depression or anxiety. Already, well before the pandemic hit, it was estimated that half of the population will experience a mental health condition at least once in their lifetime and the economic costs of mental ill-health amounted to more than 4% of GDP annually. Good mental health, on the other hand, can boost people’s resilience to stress, help them realise their goals and actively contribute to their communities. Positive mental health, or having high levels of emotional and psychological well-being, is also increasingly being recognised as policy target in its own right by health and other government agencies across the OECD.

Mental health is a vital component of people’s well-being, and measuring it is essential to monitor what ultimately matters to people. The aim of this report is to encourage official data producers to collect data on population mental health outcomes more frequently and in an internationally harmonised manner. Considering all aspects of mental health, ranging from mental ill-health (which may or may not include a diagnosed mental health condition) to positive mental states, can provide new avenues for a proactive rather than reactive design of mental health systems and services, and it can open up space for policy to focus on both reducing illness and promoting people’s flourishing. Collecting data on mental ill-health and positive mental health in household, social and health surveys would yield a more complete picture of mental health and help to better understand the drivers and policy levers for improving it.

A variety of tools are available for monitoring population mental health, ranging from administrative data to different types of survey questions. Although many OECD countries began collecting new or additional mental health data during COVID-19, official data producers were already active in this space well before the pandemic started. However, there is room for improvement by increasing the frequency of (survey) data collection, diversifying the types of indicators used to cover the full spectrum of mental health, and expanding the international harmonisation of existing measures. Here, data collectors could: (1) beyond screening tools focusing on symptoms of depression, expand use to those including symptoms of anxiety as outcome measures; (2) move towards collecting harmonised information on affective and eudaimonic aspects of positive mental health; and (3) explore using single-item questions on general mental health status across surveys.

All OECD countries currently measure population mental health, yet use a variety of tools to capture a multitude of outcomes. In order to improve harmonisation, this chapter poses a series of questions that highlight the criteria to be considered when choosing appropriate survey tools. These criteria include statistical quality, practicalities of fieldwork and data analysis. Overall, there is strong evidence supporting the statistical properties of the most commonly used screening tools for the composite scales of mental ill-health and positive mental health. Four concrete tools (the PHQ-4, the WHO-5 or SWEMWBS, and a question on general mental health status) that capture outcomes across the mental health spectrum are suggested for inclusion in household surveys in addition to already ongoing data collection efforts.