Seasonal change in Danish birth weight data (combined results for boys and girls) for three years (1973, 1988 and 1998), and fitted seasonal change based on a J-shaped exposure-risk relationship and a shifting population exposure over time. The first row of figures shows the hypothesised J-shaped exposure-risk relationship and the percent of the population in the low versus mid-high exposure groups. The second row of figures shows the estimated seasonal risk based on the observed data (solid line) and the estimated risk based on the J-shaped exposure-risk relationship (dotted line).
McGrath et al. BMC Medical Research Methodology 2007 7:45 doi:10.1186/1471-2288-7-45