One distinctive element in providing a history of past illness relates to the intellectual gymnastics involved in conceptualizing long-term personal information. For example, most patients can tell whether they are currently in pain. Ask the same patient whether he or she was in pain a year ago, however, and an accurate reply is not as easy (especially if the patient is sick right now). Such difficulties in conceptualizing the past can explain, for example, why patients often have trouble determining whether their knee pain has progressed to the point where surgery is warranted.3,4
In general, people are better at remembering events and actions rather than thoughts and intensities.
A particular source of confusion in the past medical history relates to specifying the relevant time interval for the patient. The concept of “the present” is unambiguous, whereas the concept of “the past” can have a murky boundary. Although one might imagine that errors would be symmetrically distributed around the truth, the dominant error is to assign a date to an event that is more recent than the actual occurrence. This bias, called the “telescoping effect,” has the net effect of overestimating the frequency of repeated events and exaggerating the acuteness of unique events. For example, a patient may count a tetanus vaccination from 14 years ago as being within the past decade and may thereby decline a booster dose.
Telescoping effects imply that items that are outside the boundary are inappropriately included in the reference time interval. For example, residents of Seattle were interviewed 6 months after the eruption of the Mount Saint Helens volcano.5
Those asked “In the last 6 months, did anyone try to rob you?” were more likely to report an event than those asked “Since the eruption of Mt. St. Helens, has anyone tried to rob you?” (9.2% v. 1.5%, p
< 0.05). Later verification found that almost all the events mentioned by the first group had occurred prior to the designated 6-month interval. This study shows the telescoping effect, namely, a 6-fold overreporting, and also shows that one way to reduce the bias is to avoid calendar dates and use salient landmarks to aid perspective. In medicine, salient landmarks could include major holidays, life events and other milestones meaningful to the patient.
Misunderstandings concerning a past medical history may also occur because a lot of questions are asked in an extremely arbitrary order, and the sequence of 2 questions can change a person's responses. In one study, for example, college students were asked how happy they felt and how often they were dating.6
Half were asked about their happiness before the dating question: the responses showed no correlation (r
= -0.12, p
= 0.33). In contrast, the other half were asked about their happiness after the dating question: their responses showed a high correlation (r
= 0.66, p
< 0.001). One might draw different conclusions about the link between dating and happiness from these 2 statistics. Similarly, patients' descriptions of their exercise capacity and their fatigue might change depending on which question was asked first.
Several factors can cause a person's interpretation of one question to change depending on prior questions. For example, personal experiences are not always immediately remembered, so that a preceding question might stimulate selective memories that colour subsequent responses. Whatever the explanation, medical histories are vulnerable to similar problems because the physician usually asks many questions and needs to exercise judgement about their sequence. Another physician might obtain different answers simply by phrasing questions slightly differently or by following an alternative line of inquiry. One way to double-check for such interactions is to deliberately ask the same question a few times in different ways at different points in the history.
Textbooks emphasize that questions should be sequenced in a sensible manner. For example, asking about alcohol is difficult at the start or finish of the history. At the start, it creates an image of a physician anxious to find blame. At the finish, it leaves the patient with a disturbing last impression. Asking about alcohol in a few different ways in the middle of an interview is a way to obtain a reliable response. Yet doing so requires tact because the physician's approach can be misconstrued as inattentive or overly suspicious. A failure to check for inconsistencies, however, may be the more common mistake.7