Figure 3. Incidence Rate per 1000 Person-Years of Alopecia Areata (AA) by Sex and Age Group From 2016 to 2019.

Individual weights in each year (2016-2019) were assigned using data from the American Community Survey based on census division, age, sex, and policy holder status. Incidence rate was calculated as the number of patients who had at least 1 inpatient or outpatient claim with a diagnosis for AA during the year of analysis but not the year prior divided by the total patient-years of continuous enrollment during that period. Wilson score intervals are shown. Changes in annual incidence rates from 2016 onward were estimated using weighted Poisson regression models with a log link function, with incident case counts as the dependent variable, the log of the population at risk included as an offset term, and binary indicators for calendar year included as covariates.