Statistical methods
Age trends in incidence rates were tested by Cochran-Armitage trend tests. Associations of categorical variables were tested by the Fisher exact test. Differences of medians for continuous measures were tested by exact Wilcoxon-Mann-Whitney rank sum tests. Locally weighted regressions of proportions of patients with elevated iron stores were fit using generalized additive models for binomial data with a logit link function (S-Plus 6.1). Significance was accepted at alpha = .05 for 2-tailed tests.