Another major limitation was that we used self-reports of a history of hypothyroidism and a history of hyperthyroidism; while the validation studies of self-reports showed that a high percentage of all the self-reports were likely to be accurate in this population of nurses, there was likely underascertainment of thyroid disease in the population compared to if we had conducted in-person exams or measured thyroid hormone levels for all participants. This evidence concerns the gene TG and thyroiditis.