To establish that a lack of exercise causes obesity, what must a researcher demonstrate?

To establish a causal relationship between a lack of exercise and obesity, it is crucial for the researcher to demonstrate that the lack of exercise occurred prior to the onset of obesity. This temporal relationship is a fundamental criterion in establishing causation, known as the principle of precedence. By showing that lack of exercise precedes obesity, the researcher can argue that the lack of exercise is a factor that contributes to the development of obesity, rather than obesity being a condition that coincidentally occurs alongside a lack of exercise. This helps to rule out the possibility that other factors could be influencing both the lack of exercise and obesity simultaneously, allowing for a clearer interpretation of the causal link.