Colonoscopies study

The Colonoscopies study is a landmark investigation of the difference between pain as it is experienced and pain as it is later remembered. Designed by Daniel Kahneman and Don Redelmeier and carried out by Redelmeier in the early 1990s, it asked patients undergoing painful colonoscopies to report their momentary pain at regular intervals and then to judge the total pain of the procedure afterward. Its decisive finding was that retrospective memory did not add up the suffering across time. Instead, it was shaped disproportionately by the worst moment and by the way the procedure ended.

Design and Momentary Experience

The study was conducted before anesthetic and amnesic drugs became routine for colonoscopy. Patients were prompted every 60 seconds to record the pain they were experiencing, using a scale from 0, meaning no pain at all, to 10, meaning intolerable pain. The resulting profiles showed that pain fluctuated considerably within each procedure rather than remaining constant.

The comparison at the center of the study involved two patients. Patient A underwent a procedure lasting 8 minutes, whereas patient B underwent one lasting 24 minutes; the final reading of zero pain for patient B was recorded after the procedure had ended. The wider sample contained 154 patients, with procedures ranging from 4 to 69 minutes. If suffering is measured by the duration-weighted total of momentary pain, patient B clearly had the worse experience: patient B spent at least as much time as patient A at every level of pain, and the area under patient B’s pain curve was larger.

The Retrospective Judgment

After each procedure, participants were asked to rate the total amount of pain they had experienced. The wording was intended to make them reconstruct an integral of their momentary reports, as though they were adding every painful minute together. They did not do so. Statistical analysis showed that the retrospective rating was predicted by the average of the pain at the worst moment and the pain at the end.

This finding became the Peak-End Rule. Duration had no effect whatsoever on the patients’ ratings of total pain, a result identified as Duration Neglect. The study therefore separated two measures that ordinarily appear to describe the same event. The hedonimeter total, calculated from reports of momentary pain, was duration-weighted and treated every moment as part of the total. The retrospective assessment ignored the length of the procedure and gave exceptional weight to two singular points: the peak and the ending.

The contrast between patient A and patient B made the pattern vivid. Both reported a worst pain of 8 on the ten-point scale. But patient A’s last rating before the end was 7, while patient B’s was only 1. Their peak-end averages were therefore 7.5 for patient A and 4.5 for patient B. Patient B had endured the longer and objectively more painful procedure, yet patient A retained the worse memory because the shorter procedure ended at a bad moment.

From Memory to Choice

The study’s significance extends beyond the measurement of pain. It shows how the remembering self can govern later decisions even when its judgment conflicts with the interests of the experiencing self. A person who recalls an episode through its peak and ending may choose a future experience that produces a better memory rather than a better total experience.

This conflict was demonstrated more directly in the cold-hand experiment, which used painfully cold water and continuous reports from the experiencing self. Participants underwent a short 60-second immersion at 14 degrees Celsius and a long 90-second immersion whose final 30 seconds became slightly warmer, producing a detectable reduction in pain. Although the long trial was plainly worse in total duration, 80 percent of participants whose pain diminished during its final phase chose to repeat it. Their choice reflected the more favorable memory created by the ending, not a preference for less suffering overall.

The same logic clarifies the colonoscopy findings. If a patient’s future decision is based on remembered pain, reducing the peak may matter more than reducing the duration. Gradual relief may also be preferable to abrupt relief because a relatively mild ending can leave a better memory. The study thus turns a descriptive psychological result into a practical question for medical care: whether treatment should be optimized for the patient’s moment-to-moment experience, the patient’s later memory, or both.

Well-Being and Measurement

The Colonoscopies study also became part of a broader distinction between experienced utility and remembered evaluation. Experienced utility can be represented as the area under a curve of momentary pleasure or pain, giving time an essential role: two minutes of pain at a given intensity count twice as much as one minute. Retrospective evaluation follows a different weighting system, in which duration may disappear and exceptional moments dominate.

This distinction influenced later work on experienced well-being. Rather than relying only on a global question asking how satisfied a person is with life, researchers sought to measure the feelings present during successive moments or episodes. Experience sampling used random signals on a cell phone to ask what a person was doing, who was present, and how intense the feelings of happiness, tension, anger, worry, engagement, or physical pain were. The Day Reconstruction Method offered a less burdensome alternative: participants reconstructed the previous day as a sequence of episodes, reported their activities and social contacts, rated feelings on separate 0–6 scales, and supplied the beginning and ending times needed to compute duration-weighted affect.

The resulting research kept the two perspectives separate. The experience-based measure described what people felt while living through their days, whereas life-satisfaction judgments described the remembering self’s evaluation of life as a whole. Gallup World Poll data later made it possible to compare these dimensions across millions of respondents in the United States and more than 150 countries. Such work confirmed the importance of situational factors, physical health, and social contact in experienced well-being, including the strong association between a day’s feelings and contact with friends or relatives.

Scientific and Narrative Significance

The study’s enduring force comes from the precision of its contradiction. Patient B suffered more when the entire sequence of pain was counted, but patient A remembered the episode as worse because the ending was more painful. The result does not merely show that memory is imperfect; it identifies a systematic method by which memory constructs an event’s apparent value. The past is not preserved as a complete record. It is compressed around a peak and a conclusion, and that compression can determine what people later choose.

The broader research program also places the finding within a challenge to intuitive judgment. Paul Meehl’s comparisons of expert impressions with simple statistical formulas showed that human judgments are often inconsistent in complex, low-validity environments, while formulas return the same result from the same input. The colonoscopy study reveals a related instability in self-evaluation: the experienced sequence and the remembered summary are not interchangeable. Together, these findings question the assumption that a confident overall judgment necessarily represents the underlying evidence.

The Colonoscopies study therefore functions as both an experiment and a conceptual turning point. It gives concrete form to the divide between the experiencing self, which undergoes every minute of pain, and the remembering self, which later decides what the episode meant. Its patients supplied the evidence, but the deeper subject was how a life is scored: not by every moment in equal measure, but by the few moments memory permits to stand for the whole.