If we suggest that X causes Y, can we be sure that it is X that is responsible…

This question addresses the concept of internal validity in research methodology. Internal validity refers to the extent to which a study establishes a trustworthy cause-and-effect relationship between variables. When asking if X is responsible for the variation in Y, we are assessing whether confounding factors could explain the outcome. High internal validity ensures that observed effects are due to the independent variable rather than external influences.