Growth curves with time-dependent explanatory variables

Evidence from epidemiological research suggests that childhood exposure to solar ultraviolet (UV) radiation is an important causative factor in the formation of skin cancer. A mathematical model was employed to investigate the effect of meal break times on solar UV radiation exposure to schoolchildren in southeast Queensland for the month of February. The model incorporates UV irradiances measured continuously during daylight hours for a summer month in Toowoomba (27.5°S latitude) along with the anatomical distribution of UV to specific body sites measured with polysulphone UV dosimeters. The polysulphone dosimeters have a UV response approximating that of human skin and are calibrated for UV exposure against a calibrated spectroradiometer. This paper presents the results of the UV exposures to the nose, chin, forehead and forearm for different meal break times in schools. These UV exposures were reduced by a factor of up to 0.8 by varying the school meal break times alone. Optimisation of the existing morning and lunch break times reduced the UV exposures in the school day by a factor of up to 0.45. Results of extrapolating these results to the whole year will be discussed. (C) 2000 John Wiley and Sons, Ltd