Answer: Longitudinal study
Step-by-step explanation:
Longitudinal study is the study in which same variables are studied and analyzed over a long of short duration of particular tie.This study is used in surveys and research to determines pattern, trends, flow etc of different fields.
According to the question, Dr. Dawson is conducting a longitudinal study for researching on military veterans over 10 years of time period to determine the degradation of mental skills and ability persisting PTSD.