Caution should be exercised in drawing links between improving symptoms and unproven remedies, research warns

People tend to continue with unproven treatments even when there is no evidence that an initial marginal improvement in symptoms is anything more than a possible coincidence, a new study shows.

“I have noticed that many of my patients take unnecessary vitamins, pills or alternative medicine without sufficient evidence to support their choice, leading to a lot of distraction, wishful thinking and wasted money,” said senior study author Donald Redelmeier, a staff internist and senior scientist at Sunnybrook Health Sciences Center and professor in the department of medicine at the University of Toronto Temerty Faculty of Medicine.

“Perhaps even more concerning is a false belief that leads to a missed diagnosis that later becomes incurable.”

The study, published in the news JAMA network openedexamines “post-hoc bias,” a tendency in reasoning that causes many patients to continue receiving questionable or unreliable treatments. This bias promotes a popular misconception: that because one action preceded another later event, the first must have caused the second, since it occurred consecutively.

But medical science, the researchers note, emphasizes that the sequence of two events does not prove cause-and-effect, as coincidences are common. The implication for medical care is that a patient who improved after treatment is not necessarily a patient who improved from treatment.

Instead, other possible explanations include withdrawal from a negative activity, extra rest, or the healing powers of the body itself.

To test biases across a variety of clinical cases, the researchers conducted multiple experiments using hypothetical clinical scenarios administered by a randomized survey of pharmacists and community members.

The scenarios described a patient with fatigue or some other vague symptom who feels a little better after trying a vitamin, shampoo, sugar pill or other treatment.

“We found that most respondents suggested continuing treatment indefinitely, even though the change in symptoms could be purely random chance,” says Redelmeier, who is also affiliated with ICES and the Institute for Health Policy, Management and Evaluation in U of T’s Dalla Lana School of Public Health.

“The post-hoc bias can play havoc with patients, ultimately leading to serious disappointment – ​​and for healthcare workers, it can ultimately lead to shortages in care.”

While attributing an initial improvement in – or lack of – symptoms to a treatment is a quick and intuitive approach, the researchers say the study reinforces the need for both patients and doctors to be cautious when drawing conclusions.

“An awareness of post hoc bias will not make this go away, but we suggest that patients and doctors should think twice and consider alternative explanations.”