Both subclinical and clinical forms of thyroid disease—hypothyroidism and hyperthyroidism—have become more frequent in recent years. The NHANES III Study followed people aged 12 and above over the course of 6 years, and found that the prevalence of hypothyroidism was 4.6% (0.3% clinical and 4.3% subclinical) while the prevalence of hyperthyroidism was 1.3% (0.5% clinical and 0.7% preclinical).