Uncovering the expectancy effect: the validation of the acupuncture expectancy scale

Research suggests that expectancy may modulate the response to medical interventions, including acupuncture. However, the paucity of validated tools to measure expectancy limits rigorous evaluation. We sought to validate a previously developed Acupuncture Expectancy Scale (AES) as an instrument to measure patients' expected responses to acupuncture.

Participants were patients with stage I to III cancers seen in outpatient medical and radiation oncology clinics. They were drawn from three study cohorts that included 404 participants. We examined the reliability, validity, and responsiveness of the AES.

The scores on the AES had internal consistency (Cronbach's alpha coefficient) of 0.95 and test-retest reliability of 0.62 over 4 weeks without acupuncture treatment. Those who had previously used acupuncture had higher AES scores compared to those who were acupuncture naive (12.4 vs 9.5, P = .002). AES scores were higher in those who reported willingness to participate in an acupuncture trial compared to those who did not want to participate in an acupuncture trial (11.5 vs 8.1, P < .001). Patients who enrolled in a pilot trial of acupuncture had higher AES scores than the general outpatient population (13.0 vs 9.8, P = .02), and expectancy increased during the course of acupuncture treatment (13.0 to 16.5, P < .017).

The AES is reliable and valid, and scores appear to increase during or after prior therapy. Incorporation of AES in clinical trials and outcome studies can evaluate the role of expectancy on acupuncture outcomes.