The Japanese Decline in Secondary Sex Ratio Correlates with Percentage Change in GDP/Annum

Background: Male births occur in excess of female births. The ratio of male:female births is commonly referred to as M/F and is expected to approximate 0.515. Stress has been shown to decrease M/F due to an increased rate of male spontaneous abortions. Since Japan’s economy declined after the mid-1970s, this study was carried out in order to ascertain whether there was any relationship between M/F and annual change in percentage gross domestic product (GDP) in Japan.
Methods: Annual male and female live births were obtained from a World Health Organisation Mortality database. GDP data was downloaded as an Excel sheet from the website of the World Bank. Data for both variables was available for the period 1961-2009.
Results: This study analysed 71878631 total live births. There was an overall and abrupt decline in M/F which commenced in 1975 (0.5149, from 0.5155 in 1974), one year after the decline in percentage annual GDP growth which fell from 8.0% to -1.22 from 1973 to 1974. M/F correlated with percentage annual GDP growth (r=0.4, p=0.005).
Conclusion: M/F is increasing overall in Asia, but decreasing in Japan, as is the trend in developing countries. This country exhibits a rise in GDP change along with M/F in boom years, followed by a progressive fall in both values, which occurs almost in parallel, especially after 1980. To the author’s knowledge, this is the first time that M/F has been linked with percentage annual GDP.