Birth seasonality in Jujeño (north-west Argentina) altitude populations

Seasonality of births has been related to multiple factors, including environmental, biological and sociocultural ones, in populations of diverse geographic and cultural origin. However, the relationship between this variable of bioanthropologic interest and geographic altitude has not been adequately explored. The aim of this study was to analyse the monthly distribution pattern of birth rates in Jujeño (north-west Argentina) populations located at different geographic altitude levels. Data were provided by the Statistical Reports on Liveborns (n = 110,404) in the province of Jujuy, 1985-1992. Records were grouped by birthplace into the four geographic regions of the province: Ramal (350 m.a.s.l.), Valle (1200 m.a.s.l.), Quebrada (2500 m.a.s.l.) and Puna (3500 m.a.s.l.). Henry's coefficients of seasonality were estimated. A chi-square test for goodness of fit (chi2) was used to identify statistically significant seasonal variations. Edwards' test was used to detect simple harmonic cycles in birth distribution. Statistically significant seasonal patterns were found in the four geographic regions and they respond to a cyclic model of simple harmonic variation. The greatest Henry coefficients were observed in spring and summer in the higher regions (Puna and Quebrada). whereas they were seen in autumn and winter in the lowlands (Valle and Ramal). It is suggested that these patterns reflect the influence of environmental and socioeconomic altitude-related factors and inter-regional cultural diversity, rather than the influence of geographical altitude per se.