A replication of the relationship between elderly suicide rates and the human development index in a cross-national study

Background: A recent cross-national study demonstrated a curvilinear (inverted U-shaped curve) between elderly male suicide rates and the Human Development Index (HDI) fitting the quadratic equation y = a + bx - cx(2) where y is the elderly male suicide rate, x is the HDI and a, b and c are constants). This study used only one-year cross-sectional data on suicide rates, and suicide rates can randomly fluctuate year on year. Methods: A study designed to replicate this curvilinear relationship between elderly suicide rates and the HDI was undertaken by: (i) using one-year average of five years data on suicide rates; and (ii) using more recent data on both elderly suicide rates than used in the previous study. Data were ascertained from the World Health Organization and the United Nations. Results: There was a significant curvilinear (inverted U-shaped curve) relationship between suicide rates in males aged 65-74 years, males aged 75+ years, females aged 65-74 years and the HDI fitting the quadratic equation y = a + bx - cx(2). A similar curvilinear relationship was observed in females aged 75+ years, but the significance level only approached 0.05 level. Conclusions: The replication of the curvilinear (inverted U-shaped curve) relationship between elderly suicide rates and the HDI by using one-year average of five years data on suicide rates suggests that the observed relationship is robust and accurate.