The analyses presented in the Technical Report, "Which Centers Participate in Head Start or Public Pre-Kindergarten" characterize centers that have at least one child whose enrollment is funded through Head Start or Public Pre-K funds. This supplement to the technical report provides interested readers with technical details of the analyses, including additional information about tabulations and definitions used, as well as discussion of features of the data that affect how additional analyses might be undertaken. [For "Which Early Care and Education Centers Participate in Head Start or Public Pre-Kindergarten? National Survey of Early Care & Education. Technical Report. OPRE Report 2015-92a," see ED564119.]