Abstract:
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We examined determinants of variation in childhood nevus counts using data from two age cohorts in the study of nevi in children (SONIC). We measured inter-individual variation using the squared coefficient of variation and the Gini index and visualized the former by plotting the cumulative probability distributions of nevi under two sampling schemes. This plot provides vital information about the predictive performance of risk factors. A monotonic transformation of this plot gives the Lorenz curve and, hence, the Gini index. Thus, the two statistics are equivalent. In SONIC, the observed squared coefficients of variation in nevi were 1.5 (Gini = 0.52) and 0.74 (Gini = 0.45) for children aged 10 and 13 years, respectively. The estimated values using genetic and demographic factors were 0.5 (Gini = 0.38) and 0.39 (Gini =0.34) for children aged 10 and 13 years, respectively. Adding sun exposure increased these estimates by only a small amount. Thus, nevus development in children is under strong genetic control. Plots showed that additional risk factors for nevi remain to be identified to better predict nevi, especially in younger children.
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