Figure 1
(a) The absolute latitude at each study site extracted from the GIS.13 Patients were divided into three groups according to the summer daylight exposure (SDE) at their site: high (>75th percentile: ⩾15.5 h; n=22), intermediate (between the 25th and 75th percentiles: >15.5 to <14.3 h; n=73) and low (<25th percentile: ⩽14.3 h; n=23) SDE. (b) Distribution of the summer daylight exposure groups according to the latitude of the centres: four centres with lower SDE and nearest to the equator (low latitude), 10 sites had highest SDE and were farthest from the equator (high latitude) and 14 sites were in the intermediate latitude group. Number of patients at each site is shown. The three groups are coloured differently.
