Population Stress, Civil Unrest and the Male to Female Ratio at Birth in Chile, Argentina, Australia and Finland.

ABSTRACT

Introduction: Male live births occur slightly in excess of female births but the ratio is influenced by a very large variety of factors. This ratio is remarkably stable but may exhibit sudden shifts in response to influences such as population stress. A World Health Organisation dataset comprising annual live births by year and country was analysed not only to pinpoint outlier values but also to attempt to identify historical causes for such outliers. Methods: The WHO HFA (Health for All) mortality database was used to identify outlier M/F values. Data was analysed using chi tests and chi tests for trend. Comparison for years of interest were made against baselines of only up to five years before and after such years since M/F exhibits potentially confounding long-term secular variations. Results:  Chile There was a significant difference in M/F between the period 1967-1971 and 1972 (p<0.0001). There was a decline over 1972-1976 (p<0.0001).  Argentina Increases were noted in 1978, 1988 and 1994 (p<0.0001).  Australia M/F rose sharply in 1956 (p=0.0008).  Finland There were increases in 1962 and 1971 (p<0.0001). Discussion: Stress has been shown to affect M/F. Almost all of the observed outliers were temporally associated with political events or political decisions that influenced the respective countries’ economies. M/F ratios worldwide provide tantalising hints that even transient stress may influence this ratio, making it a sensitive indicator of overall population stress.