Answer:Longitudinal research
Explanation:Longitudinal research is a correlational research which focuses on variables and studies them over an extended period of time. It ranges from weeks to years .
How Longitudinal Research Works
This research focuses on a single group of individuals with similar characteristics and studies them over a period of time in order to see if there are any changes that can be observed over that period , for example if one wants to study how exercising improves the life of the middle adults ages 40 to 50 they will study that group for months and keeps observing the changes amongst individuals within this group.