Suicide trends in Germany from 1991-2022, considering misclassification of undetermined intent deaths – a time-series analysis.

Background: Changes over time in age-standardised death rates of undetermined intent (USDR) and suicide (SSDR), the sum of suicide and undetermined rates (SUSDR), and the USDR to SSDR rates ratio will point to variations in “hidden suicides” caused by disparities in the death registration procedures. We aim to analyse from 1991 to 2022: 1) trends and differences for suicide (SSDR) and suicide plus undetermined rates (SUSDR), 2) trends and breakpoints in the USDR to SSDR ratio. Methods: Suicide and undetermined death registration data for German inhabitants were obtained from the Federal Health Monitoring website from 1991 to 2022. SDRs were calculated and analysed by joinpoint regression analysis. Rate ratios were calculated by dividing USDR by SSDR. A time-series analysis was then applied to detect structural changes in the USDR-to-SSDR ratio. Results: In the last 32 years, SSDR and USDR declined by 41.01% and 19.55%. The trends for SSDR and SUSDR are not identical (p<0.001). The ratio of USDR to SSDR varied from 0.11 to 0.37. Breakpoints were identified in 1997, 2010, 2016, and 2005 for males. Limitations: Analyses are post-hoc, and causal relationships cannot be identified. Discussion/Conclusion: Unequal trend declines for SSDR and SUSDR could indicate hidden suicide. The breakpoint in 1997 could be due to registry variability when ICD9 gave place to ICD10; the breakpoint in 2010 could be attributed to boosted suicide awareness after national media reporting about Robert Enke’s suicide; other factors could explain the breakpoints in 2016, and for males in 2005.