In its discussion of locus of control, the text cites the british cohort study, which followed 11,000 britons over a period of two decades (gale et al., 2008). because the same sample was tracked for an extended time, the study exemplifies the use of a research design in developmental psychology.

Longitudinal

Explanation:

In research, a longitudinal research design is a type of design that involves looking at the variables for a long period of time. During this time, observations are made and repeated during the time that the experiment takes place. This way, a longitudinal research design makes comparisons over time.

In this example, the British Cohort Study followed 11,000 britons over a period of two decades. This sample was tracked during these two decades. Therefore, observations on the sample were made during all this time and this exemplifies the use of a longitudinal research design.

well considering i can't see the graph, it's probably prices