The confounding influence of sun exposure in melanoma

particularly important in causing melanoma and we have reported the results of large-scale studies of the outdoor ultraviolet (UV) exposure in schoolchildren in England and Queensland. In the English study, 90 primary schoolchildren (aged 9–10 years) were monitored with UV-sensitive polysulphone film badges over a 3-month period from midApril to mid-July, 1994, in Durham (55°N), Wallingford (51°N), and Plymouth (50°N). Corresponding monitoring in Queensland took place in 112 schoolchildren (aged 11–12 years) over a 2-week period at each site from late spring to early autumn during 1991/92 in Brisbane (27°S), Toowoomba (27°S), and Mackay (21°S). Badges were attached to clothing in the shoulder/chest region. Participants were instructed not to cover badges by clothing, and to transfer badges whenever clothing was changed. Ambient UV radiation was monitored throughout the study periods at all sites in England and Queensland. The average diurnal ambient values recorded were 14 SED (Durham), 19 SED (Wallingford), and 16 SED (Plymouth); 22 SED (Toowoomba), 38 SED (Mackay), and 54 SED (Brisbane). (The SED [standard erythema dose] is a measure of sunburning radiation: minimum erythema on the unacclimatised skin of subjects who always burn and never tan would require an exposure of about 1·5 SED, whereas in people who tan easily and rarely burn, an exposure of about 6 SED would be needed to cause minimum erythema). Although the studies were planned and executed independently and at different times, in both studies children were monitored whilst at school and at weekends, and remained in the vicinity of the radiometer sites throughout the monitoring periods. Polysulphone film photodegrades on exposure to UV and will saturate if over-exposured. Because of differences in ambient UV between Queensland and England, new badges were worn by the Australian children on each day of the monitoring period, whilst in England each child wore two badges per week, one badge Monday to Friday and another badge on Saturday and Sunday. This methodological difference ensured that badges worn by all children in the study received insufficient UV to saturate their response. In each study about 40% of badges were either not returned or rejected due to damage. Missing badges were distributed fairly evenly across all locations and both sexes minimising the likelihood of bias in the reported results. Frequency histograms of daily exposures received by the children in each study are shown in the figure. Whilst the RESEARCH LETTERS