Does suicide in New Zealand follow a semi-lunar rhythm?

Abstract

The hypothesis that lunar cycles influence human behaviour, particularly incidents recorded by police or coroners, has been a topic of public and media interest around the world for decades. While connections between lunar cycles and numerous cultural practices are well-documented, claims that lunar cycles influence crime or suicide statistics have not been consistently supported. There have been recent media claims that suicide rates in New Zealand follow a lunar cycle, correlating with the Māori Maramataka lunar calendar. Building on prior research, this study scrutinises the postulated association between lunar phases and suicide rates, for general and Māori populations. Utilising 2 decades (2000-2022) of data from the National Coronial Information System (NCIS) and the New Zealand Ministry of Health - Manatū Hauora, the study employs Poisson regression models and cosine curve analyses. Results reveal no significant correlation between lunar phases and suicide rates for the overall population or the Māori sub-group. The absence of a lunar effect persists across univariate and multivariate analyses, incorporating annual, seasonal and day-of-the-week variations. Contrary to claims linking lunar phases to Māori suicide rates, this study provides a robust analysis of comprehensive suicide data. While acknowledging potential limitations, such as the diversity among Maramataka systems and unaccounted external factors, this study emphasises the need for evidence-based practices in mental health interventions. Further research is warranted to explore potential lunar influences on less severe mental health indicators and to substantiate claims supporting traditional Māori Maramataka-based treatments.