Fig. 2

Monthly birth rate in the Czech population. a Number of new-born boys and girls per month during 1978–1982. Solid line – boys, dashed line – girls. b The percent of the mean monthly number of new-born girls + boys of a control group through 1964–2000. The horizontal lines represent the upper and lower limit of a 95% confidence interval indicated here by a grey strip. The confidence interval comprises the values that do not significantly differ from the mean value. The data located above or below the grey 95% interval are significantly (p < 0.05) higher or lower than the mean value, respectively. A significant baby boom was found in March, April, and May. Such delivery timing corresponds to conception during the summer time - in June, July, and August. A significant minimum of new-borns was observed in October, November, and December, corresponding to conception during the winter time - in January, February and March. Axis x: Roman digit - month of delivery, Arabic numeral - month of conception