A research study finds that a group of participants who received relaxation training had lower exam anxiety scores than a group who did not receive training. However, the researcher suspects that the difference between groups may be caused by the fact that the participants in one group are generally smarter than those in the other. This study has a problem with

Internal Validity

Explanation:Internal validity refers to the fact that the result from a study can be trusted because they resulted exactly from what was used as a measure. This means no alternative explanation can be used to explain those findings but if there is an alternative explanation besides what was used in an experiment this means the results can't be trustworthy. If the improvements that is observed are not due to the treatment given to participants then it makes us less confident in those results . If there is less confounding (confusing factors )in a study , the internal validity will be higher and more confident one will be on that study. In the case the confounding factor is that some participants are generally smarter.