Expectations form one of the important predictors of response to treatment, especially in the case of treatments for pain. A person’s belief or expectation that a treatment will reduce their pain is thought to be part of the response to placebo – and indeed, part of the response to almost any treatment. Much of the research into expectancies has been carried out in experimental models where healthy people are given a painful stimulus, then provided with some sort of treatment along with a verbal (or written) instruction that is thought to generate a positive belief in the effectiveness of that treatment. The people we see in a clinical setting, however, are in quite a different setting – they experience pain sufficiently disruptive to their sense of well-being that they’ve sought treatment, they may not know what the pain problem is, they may have other health conditions affecting their well-being, and for some, their pain may be chronic or persistent. Do expectations have a clinically-relevant effect on their pain?
Luckily for us, a recent meta-analysis published in Pain (Peerdeman, van Laarhoven, Keij, Vase, Rovers, Peters & Evers, 2016) means the hard work of crunching through the published research has been completed for us! And given 15 955 studies were retrieved in the initial pass through the databases, we can be very relieved indeed (although only 30 met the inclusion criteria…).
What are expectations?
Before I swing into the results, it’s important to take a look at what expectations are and how they might relate to outcomes. According to Kirsch (1995) response expectancies are expectancies of the occurrence of nonvolitional responses (ie responses we’re not aware we make) as a result of certain behaviours, or specific stimuli. Kirsch points out that nonvolitional responses act as reinforcement for voluntary behaviour, so that by experiencing a nonvolitional response such as relief, joy, reduced anxiety and so on, people are likely to engage in behaviours associated with that experience again. For example, if someone is feeling worried about their low back pain, just by having a treatment they expect will help and subsequently feeling relieved, they’re likely to return for that treatment again.
How are expectations created?
Some expectations are generated within a culture – we expect, for example, to see a health professional to relieve our ill health. In general, simply by seeing a health profession, in our developed culture, we expect to feel relieved – maybe that someone knows what is going on, can give a name to what we’re experiencing, can take control and give direction to whatever should happen next. This is one reason we might no longer feel that toothache as soon as we step into the Dentist’s waiting room!
Peerdeman and colleagues outline three main interventions known to enhance positive expectations for treatment: verbal suggestion “You’ll feel so much better after I do this…”; conditioning “If I give you this treatment and reduce the painful stimulation I’ve been giving you, when you next receive this treatment you’ll have learned to experience relief” (not that you’d actually SAY this to anyone!); and mental imagery “Imagine all the wonderful things you’ll be able to once this treatment is over”.
I think you’d agree that both verbal suggestion and mental imagery are processes commonly used in our clinics, and probably conditioning occurs without us even being aware that we’re doing this.
How well does it work for people with acute pain?
As I mentioned above, expectations are used in experimental designs where healthy people are poked and zapped to elicit pain, and hopefully our clinical population are not being deliberately poked and zapped! But in clinical samples, thanks to the review by Peerdeman and co, we can see that there are quite some impressive effect sizes from all three forms of expectancy induction – g = 0.67 (95% CI 0.49-0.86). That means a good deal of support from the pooled results of 27 studies to suggest that intentionally creating the expectation that pain will reduce actually does reduce pain!
And now for chronic pain
Ahhh, well…. here the results are not so good, as we’d expect. Small effects were found on chronic pain, which is not really unexpected – chronic pain has been around longer than acute pain, so multiple reinforcement pathways have developed, along with pervasive and ongoing experiences of failed treatments where either neutral or negative effects have been experienced.
What does this mean for us as clinicians?
Probably it means that we can give people who are about to undergo a painful procedure (finger pricking for diabetes, dressing changes for ulcers, getting a flu jab) a positive expectation that they’ll feel better once it’s over because the strongest effect was obtained for people undergoing a painful procedure who received a positive verbal suggestion that the procedure would help.
Chronic pain? Not quite so wonderful – but from this study I think we should learn that expectations are a powerful force in our treatments, both individually with the person sitting in front of us, but also socioculturally – we have an expectation that treatments will help, and that’s not something to sniff at. Perhaps our next steps are to learn how to generate this without inducing reliance or dependence on US, and on helping the person recognise that they have generated this themselves. Now that’s power to the people!
Kirsch, I. (1985). Response expectancy as a determinant of experience and behavior. American Psychologist, 40(11), 1189.
Peerdeman, K. J., van Laarhoven, A. I. M., Keij, S. M., Vase, L., Rovers, M. M., Peters, M. L., & Evers, A. W. M. (2016). Relieving patients’ pain with expectation interventions: A meta-analysis. Pain, 157(6), 1179-1191.