2024/02/14
Okayama University
Keio University School of Medicine
◆ Key Points
The change in the suicide aggregation method by the National Police Agency in 2022 has affected national suicide statistics data.
After the 2022 change in aggregation method, compared to the trend over the past 12 years, the number of suicides with unknown reasons decreased by 167 cases per month, while those with identified reasons increased by 839 cases per month (total, with duplicates).
The impact of the change in aggregation method was consistently observed across seven major reason categories.
Professor Naoko Harada of the Graduate School of Health System Integration Sciences, Okayama University; Specially Appointed Associate Professor Masahide Koda of the Graduate School of Medicine, Dentistry and Pharmaceutical Sciences (Medicine); and Specially Appointed Associate Professor Shuhei Nomura of the Department of Health Policy and Management, Keio University School of Medicine, evaluated the impact of the 2022 change in the aggregation method for suicide statistics implemented by the National Police Agency. Using data from January 2010 to December 2022, they conducted an interrupted time-series analysis to investigate changes in the level and trend of the number of suicides before and after the introduction of the new method. The number of deaths with identified reasons from January 2010 to December 2021 was 274,274, and the number of deaths from January to December 2022, after the new aggregation method was applied, was 28,165. For cases with identified reasons, while the average monthly trend was 1,723 cases in 2021, a statistical analysis after the 2022 change in aggregation method confirmed an increase of 839 cases (95% confidence interval 639–1,039) compared to the trend over the past 12 years. This indicates a change in the level of the aggregated values compared to past trends.
This trend was consistent across all categories (family problems, health problems, economic and life problems, work-related problems, relationship problems, school problems, and other reasons). Regarding cases with unknown reasons, while the average monthly trend was 485 cases in 2021, there was a decrease of 167 cases (95% confidence interval -225 to -110) in 2022 compared to past trends.
While the results of this study indicate that a simple comparison before and after 2022 is no longer possible, the number of "unknown reasons" has decreased. In the medium to long term, this change is expected to contribute to clarifying the reasons for modern suicides. The results of this research were published on December 14, 2023, in JAMA Network Open , a journal published by the American Medical Association.
For the full press release, please see below.