The NIS conducts quarterly surveys in 78 Immunization Action Plan (IAP) areas which includes the 50 states, the District of Columbia and 27 urban areas with an average annual sample of 400-500 households in each area. The first phase of the NIS is a list-assisted random-digit survey which collects child, parental and household demographic information. The second phase of the NIS is a provider record check survey which collects the number of doses per vaccine and then compares these reports to the immunization schedule to determine if the child is up-to-date.