In a study published in a 2007 issue of the journal Preventive Medicine, researchers found that smokers were more likely to have used candy cigarettes as children than nonsmokers were. When hearing about this study, John responded, “But isn’t the smoking status of the person’s parents a confounding variable here?” When Karen asked what he meant, John said, “Children whose parents smoke are more likely to become smokers themselves when they become adults.” What else does John need to say in order to explain how the parents’ smoking status could be a confounding variable in this study?