The importance of methodological vigilance: Reevaluating suicide trends in Japan post‐2022

The recent review by Okada et al., titled "Suicide mortality rates in Japan before and beyond the COVID-19 pandemic era," published in Psychiatry and Clinical Neurosciences Reports, offers a comprehensive analysis of suicide trends in Japan from 2009 to 2023.1 We acknowledge and agree with their problematization of post-pandemic suicide challenges as a significant impact of the pandemic. However, we believe that it overlooks critical methodological modifications in Japan's suicide data classification that commenced in January 2022, which warrant further examination. The National Police Agency, responsible for compiling suicide statistics in Japan, revised the classification system, maintaining seven primary categories for suicide motives, but expanding the subcategories from 52 to 75.2 Additionally, from January 2022, up to four motives can be recorded for each suicide case, an increase from the previous limit of three. These modifications significantly influence the interpretation of suicide statistics and trends, particularly for analyses incorporating data from 2022 onwards. Okada et al. mention rises in the crude suicide mortality rates among males and females due to work-related issues in 2022. Nonetheless, these conclusions may not fully reflect the changes in data collection methodologies. It is conceivable that the reported rises are, in part, a consequence of the expanded subcategories and the allowance for more reasons per case. Furthermore, the literature cited by Okada et al.,3, 4 on motives for suicide, fail to address the implications of the revised suicide data classification system initiated in January 2022. This oversight casts doubt on the validity of their findings and highlights the necessity for cautious data interpretation. Our research, utilizing an interrupted time series segmented regression analysis, revealed a notable increase of 839 cases in established motives (representing 39.8% of the total) following the implementation of the new classification system.5 This substantial shift highlights the importance of accounting for methodological changes when analyzing suicide data and trends in Japan post-2022. Incorporating these methodological considerations would not only enhance the rigor of Okada et al.'s review but also offer a more nuanced understanding of the evolving suicide patterns in Japan. Such prevision is imperative as we develop and implement effective suicide-prevention strategies based on reliable and comparable data. Masahide Koda conceptualized and designed the study and drafted the manuscript. Nahoko Harada and Shuhei Nomura reviewed the draft and provided critical review for important intellectual content. Masahide Koda and Shuhei Nomura obtained funding. Shuhei Nomura supervised the project. All authors contributed to the final manuscript. This publication is supported by grants JP23K16359 from the Japan Society for the Promotion of Science and JPMJPR22R8 from the Precursory Research for Embryonic Science and Technology of the Japan Science and Technology Agency. The authors declare no conflict of interest. N/A. N/A. N/A.