what is the distinction between repeated measurements and matched items?

The distinction between repeated measurements and matched items lies in the way the data is collected and the purpose of the analysis.

Repeated measurements refer to situations where the same individuals or subjects are measured multiple times. For example, a study might measure the blood pressure of the same group of participants before and after they undergo a certain intervention. In this case, the measurements are repeated on the same individuals.

Matched items, on the other hand, refer to situations where different individuals or items are paired or matched based on specific criteria. The purpose of matching is to create pairs that are similar in certain important characteristics. For example, if we want to compare the performance of two different drugs, we might select pairs of patients with similar age, gender, and medical history, and then administer one drug to each member of the pair.

The key difference between repeated measurements and matched items lies in the nature of the data. In repeated measurements, we have multiple observations on the same individuals, which allows us to examine changes within subjects over time. In matched items, we have pairs of individuals or items with similar characteristics, which allows us to control for potential confounding variables and compare the groups more effectively.