ascertainment rates across geographic areas, and depends upon the accuracy of the population estimates generated by the U.S. Bureau of the Census and apportionment of 5-year age group data into five equal single-year groups. The analyses did not account for in- or out-migration of cases. Cases among previous Idaho residents who moved to another state prior to diagnosis were not accounted for, but cases among persons who previously resided in other states, but moved to Idaho prior to diagnosis, were counted as Idaho cases. This same limitation exists at the county level for county-specific analyses. Many of the statistics, particularly for the county analyses by birth cohort, are based upon small numbers of cases. Incidence rates based upon 10 or fewer cases (numerator) should be interpreted with caution.
None of the four Idaho counties with highest estimated exposure to iodine-131 showed an elevation in thyroid cancer cases from 1970-1996 in the birth cohort born during 1948-1958, which was estimated to have received the highest exposure to iodine-131. Although the overall female-to-male thyroid case ratios differed by birth cohort, this result was confounded by age, as the cumulative age-specific ratios are similar in each birth cohort.