Scientists caution against hasty conclusions when trying alternative remedies
A new study suggests that people tend to continue an unproven treatment when there’s only an initial marginal improvement in symptoms and otherwise no evidence to tell if it’s a potential coincidence.
"I've noticed many of my patients take unnecessary vitamins, pills, or alternative remedies with little evidence to inform their choice, leading to a lot of distraction, wishful thinking, and wasted money,” says Dr. Donald Redelmeier, senior author of the study, a staff internist and senior scientist at Sunnybrook Health Sciences Centre, and a Canada Research Chair in Medical Decision Sciences. “Perhaps even more concerning is a false belief that leads to a missed diagnosis that later becomes incurable.”
Published in the September 4th issue of JAMA Network Open, the study investigators explored a popular misconception that causes many patients to continue taking dubious, or unreliable, treatments: this is known as post-hoc bias – the idea that because one action preceded another later event, the first must have caused the second since it occurred in sequence.
Medical science, however, stresses the order of two events does not prove a cause-and-effect since coincidences are frequent. The general implication for medical care is that a patient who improved after a treatment is not necessarily a patient who improved because of the treatment. Instead, other explanations include withdrawal from an adverse activity, added rest, or the body’s own healing powers.
The researchers ran multiple experiments – using hypothetical clinical scenarios administered by randomized survey – to pharmacists and members of the community to test bias across a variety of clinical cases. The scenarios presented described a patient with fatigue, or another vague symptom, who feels a bit better after trying a vitamin, shampoo, sugar pill, or other treatment.
“We found that most respondents suggested continuing the treatment indefinitely even though the change in symptoms might be pure random chance," says Dr. Redelmeier, also a professor in the Temerty Faculty of Medicine and Institute for Health Policy Management & Evaluation at University of Toronto. "The post-hoc bias can play tricks on patients that can eventually lead to serious disappointments, and for healthcare workers, it can ultimately lead to shortfalls in care."
While attributing a patient’s initial improvement of symptoms – or the lack of – to a treatment is an intuitive and quick approach, say the study authors, the study reinforces the need for patients to be cautious about the post-hoc bias. Clinicians need to also continuously re-assess patients and resist the bias to assume that a patient who improves after a treatment is not necessarily due to the treatment itself.
Similarly, a lack of improvement in symptoms can lead patients to discontinue treatment too soon, they say. “An awareness of post-hoc bias will not make it disappear, however we suggest patients and clinicians need to think twice and stay mindful of alternative explanations,” adds Redelmeier, also a senior scientist at ICES.
