A Preliminary Path Analysis of Expectancy and Patient-Provider Encounter in an Open-Label Randomized Controlled Trial of Spinal Manipulation for Cervicogenic Headache
Received 29 July 2009; received in revised form 25 August 2009; accepted 8 September 2009.
Abstract
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 (β) 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 (|β| = .46-.59). Expectations had little effect on pain (|β| < .15). The patient-provider encounter had a weak effect on pain (|β| = .03-.27) and on subsequent confidence in treatment success (|β| = .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.
aDean of Research, Center for Outcomes Studies, Western States Chiropractic College, Portland, Ore
bResearch Professor, Department of Family & Community Medicine and Program in Integrative Medicine, University of Arizona, Tuscan, Ariz
cAssistant Professor of Research, Center for Outcomes Studies, Western States Chiropractic College, Portland, Ore
Submit requests for reprints to: Mitchell Haas, DC, Center for Outcomes Studies, Western States Chiropractic College, 2900 NE 132nd Avenue, Portland, OR 97230
ABSTRACT