Final answer:
The independent variable in the study is 'Ankle sprain or not' as it reflects the condition being manipulated to observe its effect on the dependent variable, vertical jump height. The study aims to determine the effect of a history of ankle sprains on athletes' performance in power generation as demonstrated through vertical jump tests.
Step-by-step explanation:
In the described research study, the goal is to assess whether the power athletes can generate, as indicated by vertical jump scores, varies according to their history of ankle sprains. The independent variable is 'Ankle sprain or not.' This is because the study is examining the effect of having had an ankle sprain versus not having one on the dependent variable, which is the vertical jump height. The researchers are controlling or changing the variable of ankle sprain history to observe its impact on vertical jump performance among athletes.
It's important to note that in a properly designed experimental study, the independent variable is the only factor that should differ between the control and experimental groups to ensure that any observed effects on the dependent variable can be attributed to the independent variable. Thus, when such manipulations are not ethical or possible, as in some quasi-experimental setups, observational studies or surveys are utilized where the independent variable is not manipulated by the researcher, but rather natural variations in that variable are studied in relation to the dependent variable.