Blinding protocols, treatment credibility, and expectancy: methodologic issues in clinical trials of osteopathic manipulative treatment.

CONTEXT In testing an experimental new drug or therapy, the gold standard in biomedical research for determining treatment efficacy is the randomized controlled trial (RCT). In pharmaceutical trials, inert placebos are an easily administered control that facilitates blinded comparisons. In clinical trials that study the effects of manual interventions, researchers must carefully consider their use of treatment control models. Choosing credible controls that will minimize bias in osteopathic manipulative treatment (OMT) clinical trials poses unique challenges to researchers because of heterogeneous OMT methods and practice. OBJECTIVE To compare the treatment credibility of sham manipulative treatment and untreated controls to active OMT. METHODS Subjects recruited for an OMT clinical trial for chronic low back pain completed a treatment-credibility rating scale comparing two written descriptions of the study interventions offered. The scale was administered to subjects before trial entry and at 6-month follow-up. Scale scores were used to compute credibility ratios for both intervention protocols (ie, OMT vs sham manipulative treatment). Repeated measures analysis of variance was used to assess changes in the credibility ratio over time, including the measurement of study group and time main effects, as well as study group x time interaction effects. RESULTS Subjects (N=91) perceived OMT as a more credible therapeutic option than sham manipulative treatment both at trial entry and at 6-month follow-up (P<.05). Among subjects completing the study protocol (n=66), there were no changes in perceived credibility of the study interventions over time. There were no significant differences in the credibility ratio among study groups (P=.64) or over time (P=.79). In addition, there were no significant study group x time interactions (P=.59). CONCLUSIONS In clinical trials, OMT may be perceived by subjects as a more credible treatment alternative than many control procedures. Treatment credibility can interact with subject expectations and study design in complex ways. When analyzing the treatment effects of OMT, investigators must consider the effects of these two subjective elements when competing interventions are offered and subjects are asked to self-report data. Study design should be optimized to equalize these effects among interventions.