The only way to establish a cause-and-effect relationship between two variables is to conduct a(n) ________.

The only way to establish a cause-and-effect relationship between two variables is to conduct an experiment.

In an experiment, researchers manipulate one variable (the independent variable) to observe the effect on another variable (the dependent variable), while controlling for extraneous factors. This controlled approach allows for a robust analysis of the relationship, thereby providing evidence to support causal inferences. Observational studies or correlational research, while useful, do not adequately establish causality as they cannot isolate the effects of variables due to potential confounding variables. Hence, experiments are essential for accurately determining cause-and-effect relationships.