When data are missing because a student was absent or chose not to answer, we take our best guess concerning what the student would have answered based on their other responses. This is called imputation. Typically, a students’ previous responses are simply carried forward. For example, if they “Agree” with a statement last time, we assume they would “Agree” again next time. This type of imputation stabilizes the data. It ensures that any changes you see on reports are the result of changes in students’ responses, not merely an artifact of who happened to respond to a given survey.