Arbitrary Coherence in Theoretical Decision Making About Surgical Training: The Effect of Irrelevant Subliminal Anchoring

Objective The extent of surgical training given to undergraduates is variable and the decisions taken on the adequacy of the amount to be delivered are often made using little evidence. Therefore, these decisions are vulnerable to bias. Arbitrary coherence is a recently recognized behavior that can be induced by influencing subjects to anchor their answers to a series of questions to an unrelated anchor. We set out to assess the impact of arbitrary numerical anchors on answers given to questions concerning surgical training. Design Prospective Anchoring Study. Setting Nonclinical environment. Participants A group of 41 fourth year medical students. Main Outcome Measures Each participant was asked to write the last 2 digits of their mobile telephone numbers on the proforma. This was used as an arbitrary anchor to their decisions. They were then asked a series of questions, the answers to which required an estimate to be made. Results There was a statistically significant correlation (r = 0.36, p = 0.04) between the mean of the answers given by each student and the value of the last 2 digits of their mobile telephone number. Despite the fact that the students knew that these numbers could not be related to the questions that were asked, they were influenced by them in their responses. Conclusions The introduction of a subliminal anchor affects decision making in participants who are given questions where estimation is required. Simple anchors will substantially sway responses in a subliminal fashion. This pilot study shows how powerful this effect can be. This effect is under-recognized and may be the source of considerable bias in research into training needs. Steps should be taken to guard against this effect in similar surveys.