The power of belief: understanding the Belief Effect

Associate Professor Vince Kelly,  QUT School of Exercise and Nutrition Science

Two people receive exactly the same treatment from equally qualified health practitioners. They have the same condition, follow the same treatment plan and are given the same advice. Yet one recovers quickly while the other struggles to improve.

Why?

Most of us assume the difference lies in the treatment itself. But decades of research suggest another powerful factor also plays a role. People's beliefs about the treatment they are receiving can also influence the outcome. This isn't about wishful thinking or simply "being positive". Beliefs can shape health outcomes through interacting psychological and biological processes.

Much of what we know about belief comes from research on the placebo and nocebo effects. A placebo effect occurs when positive expectations help improve a person's response to a treatment. Nocebo effects occur when negative expectations have the opposite effect.

For many years, researchers treated these effects simply as something to control for in clinical trials so they could determine whether a treatment really worked. But that view has changed.

Studies now show that placebo and nocebo effects involve real changes in the body and brain. Beliefs can shape how people interpret symptoms, respond to treatment and engage in behaviours that influence recovery.

These discoveries raise a bigger question…

To understand how beliefs shape treatment outcomes, our research team reviewed 26 studies from medicine, physiotherapy, pain management, psychology, and sports science. Rather than focusing on a single treatment or condition, we looked for common patterns across the research. Our goal was to understand what influences whether people believe a treatment will work.

Five domains emerged from the evidence.

Individual characteristics – people’s previous experiences, expectations, and personal outlook influence how effective they believe a treatment will be.

Practitioner characteristics – how practitioners communicate, the confidence they project, and whether they appear knowledgeable can influence what people believe about their treatment.

Individual-practitioner relationship – trust, rapport, and a shared understanding between the practitioner and the individual can influence how strongly people believe the treatment will work.

Intervention characteristics – how a treatment is explained, presented, and even labelled can influence how effective people believe it will be.

Setting characteristics – the environment where treatment takes place, from the clinic itself to the people in it, can shape people’s beliefs about their treatment.

Together, these domains offer the first unified framework for understanding belief across health disciplines.

We've named this framework the Belief Effect. The Belief Effect is a unifying framework that integrates several concepts that have traditionally been studied in isolation, including placebo and nocebo effects, expectations, treatment credibility, and self-efficacy.

The Belief Effect proposes that outcomes are influenced not only by the treatment itself, but by how strongly an individual believes that the treatment will work. It's shaped by what practitioners say and how they say it, their tone, body language and confidence. It's shaped by a person's previous experiences with treatment, good or bad. It's shaped by the treatment itself, including how it looks, how it's framed and what it's said to do. And it's shaped by the environment in which the treatment takes place, from the cleanliness of a clinic to the design of a consultation room.

By bringing these elements together, the framework may help explain why identical treatments can produce different outcomes in different people.

Belief may be the missing variable.

The Belief Effect positions belief not as a passive by-product of treatment, but as an active component shaping health and performance outcomes.

We are not suggesting that belief can replace effective treatment. A clinically proven treatment doesn't suddenly stop working because someone is sceptical of it, and belief alone won't cure a fracture or clear an infection. Our findings suggest that belief is another part of healthcare that practitioners can actively shape, alongside the treatments themselves.

This has real practical value. Simple changes, like how a practitioner explains a diagnosis, the confidence in their tone, the trust built during a consultation, or the comfort of a treatment environment, may help people get more benefit from interventions that already work. None of these changes require new technology or additional resources, just greater awareness of their impact.

Treating belief as part of the intervention, not an afterthought, may be one of the simplest ways to make existing treatments work better.

Vince Kelly is an Associate Professor specialising in strength and conditioning and sport science research. With a distinguished academic background, he has authored five book chapters and over 90 peer-reviewed papers covering various aspects of sport performance, strength and conditioning, recovery, and sport nutrition.

Read the full study, published in the Journal of Psychosomatic Research, online.