Valuable insights provided by the latest New Zealand Health Survey, yet comprehensive mental health and addiction data is still urgently needed

The Ministry of Health recently released the results of the New Zealand Health Survey (NZHS) mental health and problematic substance use module.

The findings suggest a large increase in the proportion of adults reporting high anxiety and/or depression symptoms over the last 5 to 6 years. Increases are also seen in moderate to high use of some drugs for both younger and older age groups, while problematic alcohol use appears to have declined.

This survey ran in the 2016/2017 and 2021-2023 NZHS, and samples approximately 12,000 adults aged 15 and 3,500 children aged 2-14 years (sample sizes vary depending on the year the survey was conducted).

Cross-sectional, repeated measure surveys, like the New Zealand Health Survey enable us to look at population-level trends in key indicators. The measure stays the same, but the people participating in the survey usually change because households are chosen at random each time the survey is conducted¹.

The NZHS provides valuable insights to understand the potential need, and see trends over time. However, they are unable to provide a reliable estimate of the prevalence of health conditions, the context in which these symptoms are experienced, and the impact on the person, whānau and communities.

This is in part due to the use of brief screening tools, as well as sample sizes, which limit further sub-group analysis.

The NZHS mental health and substance module uses the Generalised Anxiety Scale (GAD-7), the Patient Health Questionnaire, (PHQ-9), and The Alcohol, Smoking, and Substance Involvement Screening Test, ASSIST).

These are measures developed for and used in New Zealand clinical practice. As the name, screening tool suggests, screening tools are designed to cast a wide view of mental health and substance use experiences. From this, people who score high on these scales can be offered follow up for more in-depth conversations to better understand their experiences, and what support is needed.

Used in population surveys however, they are likely to overestimate the prevalence of mental health conditions or substance use disorders. Furthermore, feelings of distress, anxious and sad thoughts often have peaks and troughs in populations, without there being similar rises in the underlying prevalence rates of health conditions.

So, whilst such measurement tools can be useful to understand the potential need and see trends over time, they are unable to provide a reliable estimate of the prevalence of mental health conditions, the context in which these symptoms are experienced, and the impact on the person, whānau and communities.

The mental health and problematic substance use module certainly provides greater insights than the standard NZHS but there are no questions to understand for example experiences of problematic eating, or psychosis symptoms.

This more detailed information is crucial to plan and invest in mental health and addiction supports and services. Also needed are different approaches to sampling from the population, to ensure representation of priority groups, particularly groups who are often underrepresented, and mispresented in research and current data.

Te Pou are partnering with many organisations and researchers calling for investment in large-scale population studies with a dedicated focus on mental health, substance use and addiction.

We are also advocating for research to be conducted in a way that is strengths-based, upholding lived experience values and perspectives, advancing hauora Māori, and advancing the health and wellbeing of communities facing persistent health inequities in Aotearoa New Zealand.

Te Pou, with research and sector partners, are conducting technical design work, so we can develop and implement world leading prevalence studies.

For more information on this work and get involved see: Understanding population mental health and substance use | Te Pou

To view the Ministry of Health mental health and problematic substance use report go to: Mental Health and Problematic Substance Use | Ministry of Health NZ

1. Footnote: Cross-sectional studies complement longitudinal studies, like Growing up in New Zealand, where the people in the study stay the same, and are followed over time.