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It has been reported that sex ratio at birth (SRB; the ratio of male to total live births) in Europe declines with increase in latitude. 1 However, the same authors observed that changes in SRB by increasing latitude in North America compared to Europe are the reverse, and they could not explain this finding. 2 The aim of the present study was to test two null hypothesis that there are no differences in the ratio of male births to total births in Iran associated with either geographical latitude or altitude.
The annual number of live births by sex for the period 20 March 1993 to 19 March 2004 (1372 to 1382 Hejirae Shamsi, Iranian calendar) was obtained from the Annual Statistical Book of 27 provinces. (It should be mentioned that all provinces were included in the study except East Azarbaijan, because the data was not published for the study period.) A total of 5 294 495...