In contrast, the psychometric tradition relies on self-reports of patients to usually close-ended questions. It is assumed that the response to any one question is subject to error: the person may misinterpret the item, respond in a biased manner, or make a mistake a mistake in transcribing his or her reply to the answer
Sheet. The effect of these errors is minimized in a variety of ways. First, each item is screened to determine if it meets certain criteria. Second, the focus is on the consistency of the answers across many items, and for the most part, disregarding the responses to the individual questions. Last, the scale as a whole is checked to see if it meets another set of criteria.