Kelsie's interests are best measured using the ______ design.
This refers to the repeated observations of the same variables to check for changed behavior over a long or short time frame
With this in mind, we can see that because Kelise is making research on how the age of maturity has an effect on the psychological developments of adolescents over time, then she is using the longitudinal design.
Read more about longitudinal design here:
https://brainly.com/question/25681723