The data collection for Sweep 1 of the Millennium Cohort Study was carried out using a Blaise CAPI questionnaire. Additional coding and editing were done on the Blaise data post-fieldwork. These coding and editing instructions were developed by researchers at NatCen in consultation with researchers at CLS. The coding and editing was carried out by NatCen’s freelance panel of trained coders. Supervision and quality control was done by the Green Team from NatCen’s operations department along with researchers from NatCen were necessary.