The National Immunization Survey is conducted by the National Center for Immunizations and Respiratory Diseases and the National Center for Health Statistics at the Centers for Disease Control and Prevention. It began in April 1994 in order to collect data on childhood immunization coverage. It uses a list-assisted random-digit-dialing telephone survey methodology of household respondents, and a mailed survey to children’s health care providers. The target population for the survey is children aged 19-35 months at the time of the interview, and the mail-in portion of the survey collects data on all current recommended vaccines and doses. In 2011, a dual-frame sampling design with independent samples drawn from landline and cell-phone sampling frames was used in order to stay up-to-date with the rise of cell-phone-only households. In total, the survey produced complete interviews for 24,013 children, and adequate provider data for 17,004 of those children.