INCMIL is part of the Family Resources supplement that provides information on individuals' health benefits, amount of coverage and income received from employment, welfare benefits, public assistance, and savings.

Questions in the Family Resources supplement are different from those in the core survey in terms of the content and the treatment of missing data. Questions in the Family Resources were normally asked of the month prior to the interview while the core survey asked of the last calendar year. All missing data in the Family Resources supplement were imputed by NHIS and users can refer to the imputation flag variables to identify persons with imputed data.