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Investigating the path from expectancies to outcome



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A considerable number of studies in many areas of medicine have suggested there is a link between patients’ expectancies for recovery and health outcomes[1,5,6]. A patient that expects that the treatment will help them recover, is more likely to recover than a patient with lower expectations. These relationships are found in both (chronic) pain and non-pain conditions and for many treatment outcomes including; recovery, return to work, pain intensity, functioning, and also wound healing.

Although this relationship is potentially of great value for clinical practice, it is also very complex and many questions are still unanswered. In a previous blog post Steve Kamper already introduced this fascinating area of research and outlined some of the questions that need further attention.

We recently published a paper in Pain[4] in which we studied one of the possible pathways or mechanisms that link expectations to outcomes. We thought it was worthwhile to dig deeper into this ‘how’ question because if we understand how expectations influence health outcomes we may better use and benefit from this relationship.

Perhaps the most frequently-investigated pathway linking expectancies to pain is via the body’s own internal pain relief mechanism, endogenous opioid production[2].  Much of this research has been conducted in the context of understanding placebo effects using experimental pain paradigms. In these studies volunteers are given a placebo pill (or other placebo treatment) together with a verbal suggestion that this ‘treatment’ protects them from feeling pain which creates strong expectations of pain relief. In such studies often those who are given a placebo treatment and verbal suggestion experience less pain than those that weren’t (e.g. [3] and [7]). It is important to note however, that the volunteers are typically healthy people who are exposed to a painful stimulus in a safe environment as part of the experiment.

However, clinical situations are typically more complex than experimental pain studies and other mechanisms may play a role as well. The behavior of the patient may be one of those mechanisms. One of the behaviors that is important in the treatment context is adherence to treatment. We studied whether the relationship between patients’ expectancies about treatment outcome and the actual outcome was mediated by adherence to therapy.

We used data from a large clinical trial[8] in which patients suffering from acute low back pain were randomly assigned to either placebo paracetamol or real paracetamol. In this trial no differences were found between the groups suggesting that paracetamol is no more effective than placebo for treating acute low back pain. In this population however, there was a relationship between expectancies and recovery. Those who expected more benefit from the paracetamol had higher chance of full recovery and a faster decrease in pain than those who expected less benefit.  This relationship was the same whether the patients were in the paracetamol group or the placebo group.

We examined how much of the relationship between expectancies and recovery could be explained by the fact that those expecting more benefit also adhered better to the treatment regimen. We found that this was a small percentage. (3.3% of the relationship between expectancy and time to recovery and 14.2% of the relationship between expectancy and longitudinal change in pain could be explained by adherence to treatment).  This suggests that although adherence played a small role, there are one or more other pathways that explain the relationship between what patients expect and their outcomes. These might include the body’s own pain relieving mechanism as described above, or the possibility that patients who expect positive outcomes are more likely to observe small signs of recovery while they ignore negative outcomes.

There remains much to learn about the mechanisms linking expectancy and outcome in clinical situations. Some possible directions include understanding whether our findings are generalisable to other clinical populations and treatment types, and investigating the influence of the many other hypothesised mechanisms to find out their relative importance.

About Tsjitske Haanstra

Tsjitske HaanstraTsjitske Hanstra completed a Bachelors in Nutrition in the north of the Netherlands before she moved to Amsterdam to complete a research master’s degree in lifestyle and chronic disorders (epidemiology).  A research internship at Maurits van Tulder’s low back pain research group got her interested in musculoskeletal and pain disorders. Shortly after finishing her master’s degree, she started a PhD on the role of patients’ expectations in treatments for (primarily) musculoskeletal disorders.  She will defend her thesis entitled “Patients’ expectations: determinants, mechanisms and impact on clinical outcomes” in public at the VU University Amsterdam, 27th of November 2015. Tsjitske currently works as a policy advisor and postdoctoral researcher in orthopedics.

Reference List

  1. Auer C, Glombiewski J, Doering B et al. Patients’ Expectations Predict Surgery Outcomes: A Meta-Analysis. Int.J.Behav.Med. 2015.
  2. Colloca L, Miller FG. Harnessing the placebo effect: the need for translational research. Philosophical Transactions of the Royal Society B: Biological Sciences 2011;366:1922-30.
  3. De Pascalis V, Chiaradia C, Carotenuto E. The contribution of suggestibility and expectation to placebo analgesia phenomenon in an experimental setting. Pain 2002;96:393-402.
  4. Haanstra TM, Kamper SJ, Williams CW et al. Does adherence to treatment mediate the relationship between patients’ treatment outcome expectancies and the outcomes pain intensity and recovery from acute low back pain? Pain 2015.
  5. Iles RA, Davidson M, Taylor NF et al. Systematic review of the ability of recovery expectations to predict outcomes in non-chronic non-specific low back pain. J.Occup.Rehabil. 2009;19:25-40.
  6. Mondloch MV, Cole DC, Frank JW. Does how you do depend on how you think you’ll do? A systematic review of the evidence for a relation between patients’ recovery expectations and health outcomes. CMAJ. 2001;165:174-9.
  7. van Laarhoven AI, Vogelaar ML, Wilder-Smith OH et al. Induction of nocebo and placebo effects on itch and pain by verbal suggestions. Pain 2011;152:1486-94.
  8. Williams C, Maher C, Latimer J et al. Efficacy of paracetamol for acute low-back pain: a double-blind, randomised controlled trial. Lancet 2014.
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