Related Experiment Video
Updated: Jun 16, 2026
A Randomized, Sham-Controlled Trial of Cranial Electrical Stimulation for Fibromyalgia Pain and Physical Function, Using Brain Imaging Biomarkers
Published on: January 5, 2024
A preliminary path analysis of expectancy and patient-provider encounter in an open-label randomized controlled trial
Mitchell Haas1, Mikel Aickin, Darcy Vavrek
1Dean of Research, Center for Outcomes Studies, Western States Chiropractic College, Portland, OR 97230, USA. mhaas@wschiro.edu
Objective:
The purpose of this article was to present a preliminary model to identify the effects of expectancy of treatment success and the patient-provider encounter (PPE) on outcomes in an open-label randomized trial.
Methods:
Eighty participants with chronic cervicogenic headache (CGH) were randomized to 4 groups: 2 levels of treatment dose (8 or 16) and 2 levels of therapy from a chiropractor (spinal manipulation or light massage). Providers were instructed to have equal enthusiasm for all care. Structural equation modeling with standardized path coefficients (beta) was used in a path analysis to identify the effects of patient expectancy and the PPE on CGH pain. The model included monthly pain from baseline to 12 weeks. Expectancy and PPE were evaluated on Likert scales. The patient-provider encounter was measured as patient perception of chiropractor enthusiasm, confidence, and comfort with care.
Results:
Baseline patient expectancy was balanced across groups. The PPE measures were balanced across groups and consistent over the 8-week treatment period. Treatment and baseline pain had the strongest effects on pain outcomes (|beta| = .46-.59). Expectations had little effect on pain (abs value(beta) < .15). The patient-provider encounter had a weak effect on pain (abs value(beta)= .03-.27) and on subsequent confidence in treatment success (abs value(beta)= .09 and .12).
Conclusions:
Encouraging equipoise in the PPE and balancing expectancy across treatment groups may protect against some confounding related to the absence of blinding in a randomized controlled trial of pain. In this trial, their effects were found to be small relative to the effects of treatment and baseline values.
