The power of your expectations

This post is also available in Dutch.

Did you know that your expectations can have a profound impact on your perception, behavior, and health, as well as, test performance? Let me convince you.


Image by Michael J. Ermarth

If you believe that you can live a healthy lifestyle, you could likely achieve weight loss

To investigate the influence of expectations on weight loss, a study at Harvard University divided hotel housekeepers into two groups, and gave each group different information. They told one group that the amount of work-related movement (cleaning hotel rooms) was comparable to a good workout at the gym, whereas they did not tell this to the other group.  Even though the two groups did not differ in the amount of work-related movements, after 4 weeks, the informed group showed a decrease in weight, blood pressure and the percentage of body fat.

If you are a patient with asthma, simply thinking that you’re being exposed to an allergen could trigger an asthmatic attack

In the sixties, researchers from the medical center of Brooklyn demonstrated that a simple saline (salt) solution could both trigger or prevent an asthma attack. How was this possible? By simply having participants believe that the solution being inhaled was an allergen that stimulated an asthma attack or a medicine that prevented against attacks, respectively.  Importantly, healthy individuals and individuals without asthma who did not have specific expectations on their lung functions were not affected by this manipulation.

If you expect to know the answer, you perform better

Another study investigated the influence of expectations on intellectual performance during a computerized knowledge test. One group was led to believe that the test answers were presented on the screen at a level below their conscious awareness (e.g., certain information can be presented very quickly such that it is perceived but not consciously). In contrast, the other group was told that they would be presented with random letters below their conscious awareness. In actual fact, both groups were presented with random letters, but a simple difference in instructions led the first group to perform better on the test.

How can our expectations affect our weight, health, or cognitive performance?

These three studies show that expectations can affect whether something works or not. This effect is  known as the placebo-effect. A well known psychological explanation for the placebo-effect is the expectancy theory which states that someone’s perception and behavior can change due to the expectations he or she has with a certain situation. For example, I expect to be given the answers of a test, therefore I am less distracted by the possibility of failing and can focus my full attention on giving the correct answer. Another perspective on the placebo effect is based on the conditioning theory which proposes that previous experiences within a certain context will trigger previously associated or conditioned responses. For example “Since cats triggered my asthma attack in the past,  my neighbor’s cat will likely trigger one of my next asthma attacks’’.

Of course, based on these studies we cannot (and should not) draw conclusions such as not needing to exercise in order to lose weight, but it is clear that we need to be careful about how and when we use our expectations. Not being aware of the effects of our expectations can produce negative (or positive) impacts on our lives.

Read more

Interested to read more about placebo effects, follow our previous blogs here

Written and translated by Mahur.

Edited by Romy and Nietzsche 




+ posts

Leave a Reply

Your email address will not be published. Required fields are marked *