A psychologist working at a rehabilitation unit of a large hospitalimplements Interpersonal Therapy (IPT) for patients who undergo psychosocial rehabilitation following traumatic brain injuries. Staff and family members of patients notice that patients who work with this psychologist have much better interpersonal and social skills, and appear less depressed, as compared to the rest of the patients on the unit. The psychologist runs appropriate statistical tests comparing her patients to the rest of the unit and does find that patients in her group are significantly better with social and interpersonal skills, and they receive significantly lower scores on measures of depression. She then conducts a review of appropriate peer-review literature which confirms that IPT is in fact effective in improving interpersonal as social skills, as well as in alleviating symptoms of depression. Which type of error(s) is being committed in this case?