Dr. irwin is testing the same people repeatedly over time as part of a research study, whereas dr. jenner is comparing the performance of different people of various ages at the same time. dr. irwin is using a research design; dr. jenner is using a design.

Longitudinal, Cross-sectional

Explanation: Longitudinal research is the type of study that is done over a certain period of time on the same topic/subject.There are chances of extension of this research to even a long duration like decade .Dr.Irwin is studying the same people for some time duration which makes it a longitudinal research.

A cross-sectional study is research that includes observation as the basic factor and then analyzing information on several components. The analyzation is done in a cross sectional or transverse way with all component's perspective. Dr. Jenner is doing a cross-sectional study as she is studying analyzing the performance of various people.  

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explanation:

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