In 1961, psychologists RC Jacobs and DT Campbell conducted an experiment that revealed something interesting about human nature. They placed volunteers in a dark room with a flashing light and asked how much the light moved (even though the light was completely still). The movement, when reported, was the result of an optical illusion, but secretly some of the “accomplices” of the researchers were instructed to respond with specific amounts of movement, influencing the responses of the other participants.
The most interesting thing came later: as the original participants were gradually replaced by new volunteers, the “inherited” responses of the initial group continued to be perpetuated for generations, even when no one knew why those specific values had been chosen. An arbitrary tradition had crystallised into “collective knowledge.”
This experiment, although conducted in a controlled environment, reflects a phenomenon that permeates the health field: the persistence of practices whose origins are purely arbitrary, but which stubbornly resist scientific scrutiny and evidence-based change.
What counts as arbitrary in the healthcare context is not simply a question of questionable origins (many scientific discoveries arose from accidents or initial intuitions). A practice can be considered arbitrary when its origin is based on cultural conventions, personal preferences, or administrative decisions without scientific basis; it remains unchanged for decades despite the availability of evidence suggesting superior alternatives; and its maintenance is due more to institutional inertia than to empirical validation.
Calendar-Based Medicine?
Consider this example: why are antibiotic cycles multiples of seven days long? Cystitis, seven days. Cellulitis, 14. Prostatitis, 28. The answer is as simple as it is arbitrary. In the year 321 CE, the Roman emperor Constantine decreed that Sunday would be a day of rest for the urban population, cementing the seven-day week, which at the time coexisted with other cycles, such as the eight-day week, in Roman law.
While the standard year has 365 days because it roughly reflects the time of Earth’s orbit, and the day has nearly 24 hours due to the planet’s rotation period, the duration of antibiotic treatments essentially follows a decision similar to that of a Roman emperor (the cultural adoption of the number seven follows no biological criteria). It’s an irony that should shame us: one of the most fundamental practices of modern medicine is anchored more in Constantine’s calendar than in pharmacological science.
PSA (prostate-specific antigen) offers another example. The 4ng/ml cut-off value, used worldwide to decide on prostate biopsies, was established arbitrarily, without any basis in robust clinical studies. Today, we know that approximately 15% of men with a PSA below that cut-off will have prostate cancer, and that the very amount of samples collected during the biopsy (also defined arbitrarily) directly influences the likelihood of finding tumours.
Similarly, the recommendation to operate on hydroceles (accumulation of fluid in the scrotum) after two years of age is based on a convention without solid foundation. Why two years, and not 18 months or three years? Another decision that crystallised without adequate scientific reflection. The same can be said about routine episiotomy, which we discuss in this text.
Psychology of perpetuation
The persistence of these arbitrary practices cannot be explained solely by a lack of access to information or individual resistance to change. It is a more complex and systematic phenomenon, which so-called behavioural economics helps to unravel through concepts such as the status quo bias, the power of inertia, and the default effect.
The status quo bias reflects our natural preference for the current state of affairs. In medicine, this manifests itself when protocols are followed simply because ‘it’s always been that way’, a behaviour often reinforced by classic arguments of appeal to tradition (‘we’ve always done it this way’) and appeal to popularity (‘everyone does it this way’). Questioning the established order requires cognitive energy and professional courage that many prefer to economise on.
The power of inertia amplifies the phenomenon. Just as subscription companies default to automatic renewal, knowing that most customers won’t revisit the decision, medical protocols, once established, are rarely critically re-evaluated. A study of the Swedish pension system showed that 73% of people who opted for the default investment choice didn’t revisit their decision for 16 consecutive years, even when their retirement depended on it.
The default effect completes the trio: the tendency to accept preselected options without question. In the traditional medical hierarchy, this is amplified by the vertical transmission of knowledge, in which protocols pass from teacher to student with little or no questioning of their origins or foundations.
The availability heuristic adds an extra layer of complexity. This cognitive bias causes professionals to base judgments on how easily they can recall past experiences, rather than considering broader probabilistic evidence. In healthcare practices, this manifests itself when a professional maintains a specific practice because they ‘remember cases where it worked’ or avoids changes because they ‘have seen it fail’.
When an arbitrary practice becomes routine, the ‘success’ cases associated with it become easier to remember, creating a false perception of effectiveness. Simultaneously, due to loss aversion (the tendency to value what we lose more than what we gain), negative outcomes associated with protocol changes become remembered as examples that discourage future innovation.
Thus, a vicious cycle is formed: arbitrary practices generate selective memories that ‘validate’ them, while attempts at change are discouraged by amplified memories of potential problems. Tradition perpetuates itself not because it is effective, but because we are programmed to preserve the familiar and fear the unknown.
Structural arbitrariness
Traditional medical education functions as a perpetuation machine for these practices. By emphasising memorisation and repetition of protocols, it inadvertently creates professionals less inclined to critical questioning. The time pressure of clinical decisions reinforces this dynamic: reviewing established procedures demands time that is rarely available in everyday practice.
Legal liability reinforces resistance. Deviating from widely accepted practices can be seen as a legal risk, even when new evidence suggests superior alternatives. The result is a system that punishes evidence-based innovation while protecting conformity to traditions, even if unfounded.
Paradoxically, healthcare professionals who follow arbitrary protocols are legally more protected than those who apply the best available evidence if it diverges from ‘common sense in health’. It’s a reversal of values that transforms up-to-date scientific knowledge into a professional risk factor.
Returning to the example of antibiotic use, we often encounter the belief that one should always ‘complete the cycle’ (the one based on Constantine’s weeks). Two justifications are routinely invoked: avoiding relapses and preventing bacterial resistance. The problem is that there is no solid scientific evidence to support either assertion. On the contrary: recent studies suggest that excessive duration of antibiotic treatments may be more harmful than beneficial, contributing to bacterial resistance and unnecessary adverse effects. But the belief in the ‘complete cycle’ is so ingrained in medical culture that questioning the practice still generates discomfort and resistance.
This doesn’t mean that, as patients, we can stop taking antibiotics on our own at any time. It’s crucial to clarify: the debate over treatment duration concerns the formulation of protocols by professionals and researchers, not individual patient decisions. What we’re questioning here is not whether patients should comply with their prescriptions, but whether the protocols guiding those prescriptions are based on the best available scientific evidence.
Final considerations
The Behavioral Economics models presented here were primarily described for contexts where the consequences are financial, while in the healthcare field, the consequences involve illness and death. It is important to consider that this difference can significantly alter the manifestation of cognitive biases.
Medical practice has unique characteristics (responsibility for human life, strong regulation, logistical complexity) that foster resistance to change that transcends individual biases. Therefore, not all persistence of arbitrary practices can be explained solely by behavioural factors; resource constraints, legitimate scientific uncertainties, and systemic pressures also contribute.
Understanding these psychological and systemic mechanisms should not generate pessimism, but rather foster more sophisticated strategies for transforming healthcare practices. Recognising that resistance to change is not just a matter of ‘education’ or ‘access to information’, but a complex behavioral phenomenon, can guide more effective approaches. The implementation of Evidence-Based Medicine fails not only due to a lack of evidence per se, but also due to a failure to adequately consider psychological and structural obstacles.
Perhaps by better understanding the mechanisms that sustain unfounded practices, we can free medicine from the tyranny of its own traditions, building a practice genuinely based on evidence, critical questioning, and real benefits for patients.
This story was originally published by Revista Questão de Ciência in Brazil. It is translated and reprinted here with permission.
