Samir is conducting a correlational study, and he cannot determine whether one variable causes another. one reason for this indetermination is that the additional variables that he did not study could influence the variables he did study. this result reflects the problem with:

The answer to this question is: the third variable problem
a third variable problem is A type of confounding in which a third variable leads to a mistake in the causal relationship between two other Variable.
For example, if you a population has higher rate of cancer as they consume more tofu, it doesn't necessarily mean that tofu is the one that cause cancer.