Eight state agencies with varying MIS platforms and high quality WIC PC 2020 data completed a survey about their MIS and longitudinal data provision capabilities. The survey assessed these state agencies' MIS capabilities, as measured in six areas, to provide a longitudinal data set.

Next, we chose one state agency and worked with state agency staff and their MIS contractor to extract longitudinal data that included one record per infant or child per week from January 2014 to December 2019.

Once the data were collected, we used two matching approaches to link the records for each infant or child over time. First, we used deterministic matching where the participant ID provided by the state agency was used to link records belonging to the same infant/child. Second, for records that had more than one participant ID, we used probabilistic matching where other identifying variables (e.g., date of birth, first name, and last name) were used to match records that likely belonged to the same participant. Each potential probabilistic match was rated with a similarity score. We reviewed the probabilistic matches and compared their similarity scores to a predetermined threshold to determine whether matches were accepted.

Finally, we conducted example analyses to demonstrate the type of information that could be gained from longitudinal WIC PC data.