We found that participants’ general expectations for improvement, but not their specific expectations of chosen therapies, were significantly associated with changes in disability at 5 and 12 weeks. We also found that the association between general expectations and outcome appeared to be substantially higher in the usual care versus the choice group (see Table ).
We are aware of only 1 prior study that has evaluated the effect of patient expectations on their low back pain outcomes. In that study, general
expectations for improvement were not
found to be associated with improvement in Roland score at 10 weeks, whereas specific expectations were
associated with improvement.4
The studies, however, had important differences. Whereas our population suffered from acute
back pain, the prior study evaluated patients with chronic
back pain. The prior study was limited to 135 patients and used a 7-point Likert scale (where patients rated their expectation for recovery in 1 month from 1 [complete recovery] to 7 [much worse]) to measure general expectation. A final, fundamental difference was that the prior study randomly assigned patients to acupuncture or chiropractic, whereas our study asked patients to choose between three CAM therapies. In this light, the possible mediating effect of choice on the association between expectation and outcome (discussed below) may be relevant.
The different measures of general expectation in these 2 studies highlight the need for a more standardized approach to studying the association between patient expectations and clinical outcomes. In the systematic review performed by Mondloch and colleagues, only 2 of the 16 studies reviewed shared a common question regarding patient expectations.9
To develop a more comprehensive understanding of the complex associations between patient expectations and recovery, we need to develop validated instruments for assessing expectations and take a more uniform approach in our study designs, asking study subjects about expectations before randomization.
Whereas the differences between studies on patient expectations are noteworthy, the similarities are even more striking. In the vast majority of studies, investigators have consistently shown strong, statistically and clinically significant associations between patients’ expectations and clinical recovery.
The reason for this association remains unexplained. It could be that patients are good judges of their own illnesses and are able to accurately identify their likelihood of improving over several weeks. An alternative explanation is that there is a reporting bias such that patients who have predicted they will have significant improvement are more likely to report improvement several weeks later so as to be self-consistent. A third possibility is that higher expectations are associated with better compliance with a medical regimen that is responsible for greater improvement. It is also possible that there is something about the expectation itself that is therapeutic, akin to the placebo effect.
One of the more intriguing, albeit speculative, findings of our study is the possible differential effect of expectation on outcome in the choice versus the usual care groups (see Table ). To our knowledge, no study has ever looked at this type of effect modification. Whereas it is possible that such a difference could result from patients having strong negative associations with CAM (and thereby having their expectations dampened after being randomized to choice), this does not appear to have been the case. On average, we found that patients rated CAM therapies similar to conventional physical therapy in terms of their likely helpfulness for their current episode of back pain.
The stratified analysis could shed light on the possible etiologic scenarios outlined above. It is unlikely that the first 3 explanations—patients’ self-awareness, reporting bias, or compliance—would be dramatically different in the choice versus the usual care groups. However, it is certainly possible that the act of choosing one’s own therapy might have an impact on the 4th scenario (i.e., that the expectation itself is therapeutic). A component of positive expectation may be confidence that a health care provider will choose the appropriate intervention to heal the patient. Perhaps placing that choice entirely in the hands of the patient reduces the overall effect of the expectation. (As discussed below, patients in our study were not provided with the information, support, and dialog critical to shared decision making). Whereas this line of argument can only be conjectural based on our own research, it is worth further study.
One limitation of our study is that it did not have adequate power to evaluate whether the association between expectation and outcome was different in the choice versus usual care groups. Because an interaction term is needed to evaluate this type of effect modification, and because the interaction term is the product of 2 variables, we would have required 4 times as many subjects to maintain the same power to evaluate this question. Despite dramatically different β-coefficients for choice versus usual care (0.27 vs 0.80) even the week 12 interaction term was just short of statistical significance.
A second limitation was that the general and specific expectation questions were formatted somewhat differently, which makes a direct comparison of the responses problematic.