Survey development

The survey used in this study was developed by the authors with consideration of previously implemented instruments that examined practice patterns among chiropractors[21–24]. It included six questions intended to solicit demographic information. In addition, the survey was designed to elicit information pertaining to divergent perspectives (strata) held by chiropractors. A previous analysis of chiropractic professional identity validated a categorization system that could be used to differentiate subgroups of chiropractors based on their perceptions of the conditions they treat. In our survey, the full descriptions of the six chiropractic subgroups from this analysis[3] were used as possible answers to the question: “Which one of the following best describes the predominant view you have of the conditions you treat?” The first subgroup was defined by the term “General Problems”. Chiropractors in this category are considered to have a broad perspective on the conditions they treat that includes lifestyle and wellness issues. The second subgroup was defined by the term “Biomechanical”. Members of this category identified themselves as treating mainly musculoskeletal or neuromusculoskeletal problems including specifically low back and neck-related pain. The third subgroup combined the concerns of the first two reflecting on the conditions they treat in the context of both “General Problems” and “Biomechanical” disorders. The fourth subgroup defined themselves by combining the “Biomechanical” conditions treated and some conservative component of “Organic-Visceral” complaints. The fifth subgroup indicated that they treated “Chiropractic Subluxation”, but considered subluxation as a “Somatic Dysfunction” which is consistent with a biomechanical perspective. Finally, the sixth subgroup of chiropractors also indicated that they treated “Chiropractic Subluxation” but their view was that the subluxation was an encumbrance to the expression of human health that needed to be corrected to benefit patient well-being.

The most extreme unorthodox view relative to current scientific paradigms associated with health care was defined by a subgroup who identified themselves with the notion that the chiropractic subluxation (lesion treated) was an “obstruction to human health”. Orthodox in this instance is defined as being consistent with the notion held by a majority of North American orthopaedic surgeons that chiropractic treatment is not effective for non-musculoskeletal conditions[25]. In contrast to the unorthodox perspective, all other chiropractic subgroups are identified with musculoskeletal joint dysfunction, which may or may not include public health and lifestyle concerns but appear relatively consistent with orthodox views regarding health overall and musculoskeletal health in particular.

In order to explore the attitudes that may have import to policy making and foster potential barriers to interprofessional relations, additional questions were included regarding conditions deemed amenable to chiropractic care, chiropractic practitioner use of X-rays, and views on vaccinations. These questions were based on a previous survey of orthopaedic surgeons’ attitudes towards chiropractic, suggesting them as areas of concern for interprofessional relations[25]. For example, of the 487 surgeons who participated in that survey, approximately 81% were either undecided or agreed that “Chiropractors make excessive use of radiographic imaging”, 91% were either undecided or agreed that “Chiropractors provide patients with misinformation regarding vaccination” and 93% were undecided or disagreed that “Chiropractors treat in accordance with evidence-based practices” (p. 2821).

To evaluate chiropractors’ perspectives on these issues, our study instrument included a question to document whether practitioner use of radiographic imaging was consistent with evidence-based radiography guidelines[26]. In this question, participants were asked to select from eight choices, the reasons they would choose to X-ray a patient. Participants were categorized as not ordering X-rays in accordance with evidence-based guidelines if they chose one of the reasons for which there was no literature-based evidence.

With respect to vaccination, three vaccination attitude statements were included, based on a five-point Likert scale for each. These three questions were intended to measure consistency with current medical science[27] and the official statement of the Canadian Chiropractic Association [Association accessed, June 2012]. They provided a vaccination consistency score of up to 15, with a higher score reflecting a more negative attitude toward vaccination. Respondents were considered “negative” to vaccination if they scored 10 or higher on these questions. A score of 9 could have been achieved by responding “neutral” to all three questions. Therefore, a score of 10 definitively placed participants in the “negative” category.

To evaluate for evidence-based practices, chiropractors were asked to document which disorders on an alphabetized list of 27 complaints and diagnoses, they believed they could address the cause. This list (available on request from the authors) was compiled based on previous literature, as well as, controversial concerns that the authors were made aware of. It is understood that no list of complaints and diagnoses chosen can be exhaustive, but rather is representative of choices that might be made, dependent on practice perspective and the chiropractic subgroup. For 21 of the disorders, research evidence existed suggesting at least a basis upon which chiropractic neuromusculoskeletal treatment could be provided (though results of treatment studies may have been inconclusive or indeed negative). For six of the disorders no such basis could be determined. Participants were categorized as not treating in accordance with evidence-based practices if they chose one or more of the six disorders for which no scientific literature could be found.

Pre-testing consisted of having five practicing chiropractors complete the initial survey. These chiropractors were then interviewed in order to identify potential problems, ambiguities or confusion surrounding the questions included. Thereafter, a second group of five practicing chiropractors were asked to complete the revised survey to ensure that ambiguities and confusions had been resolved. The final version of the three-page instrument contained 16 questions that were both qualitative and quantitative in nature in which were embedded the three questions (imaging, vaccination and treatable complaints) relevant to this study. A copy of the exact questions associated with this investigation is available from the authors upon request.

Survey administration

Online directories of the provincial chiropractic licensing bodies were used to establish a list of all currently licensed chiropractors for each of the nine English-speaking Canadian provinces (BC, AB, SK, MB, ON, NS, NB, PEI, NL). Each licensing body was contacted, advised of the project and asked to verify that their online directories were representative of the licensed and practicing chiropractors in the province. A computerized random number generator was used to select a random sample from each provincial list. A total of 749 chiropractors (estimated as 12% of chiropractic practitioners nationwide), stratified proportionally across the English-speaking Canadian provinces, were selected.

The sample size was calculated based on odds ratio estimation. Since this study was designed to sample participants without knowledge of their group classifications for either the predictive variables (x-ray use/non-evidence based treatment group/vaccination attitude) or the outcome variable/group of interest (orthodox versus unorthodox) a potential sample size disparity of 1.5:1 was assumed in terms of exposed/unexposed for the dichotomous predictive variables, along with a general prevalence of 25% of the unexposed participants being classified as unorthodox. Under these assumptions and assuming a survey response rate of 50%, by distributing 700 surveys, approximately 350 would be expected to be completed and returned. This would allow the detection of odds ratios of approximately 2.0 at the 0.05 type 1 error level with a power of 0.8[28].

The survey was administered by mail from August 2010 to December 2010. In order to maximize the response rate, surveys were mailed with a personalized letter briefly explaining the purpose of the study and guaranteeing anonymity. A return addressed and postage paid envelope was also provided[29]. Each survey contained a unique tracking number that was used to monitor respondents. Additional mail-outs were sent to non-responders at 6 weeks and 16 weeks after the initial mailing. The Canadian Memorial Chiropractic College Research (CMCC), Ethics Board approved the study (REB Approval # 1006X02).

Data entry and analysis

All survey data were entered into an electronic spreadsheet by two authors, using the double data entry method to control for errors.

A logistic regression model was developed using the R project statistical software, to determine if the proponents of unorthodox views (proxied by the most extreme chiropractic subgroup – “Chiropractic Subluxation as an Obstruction to Human Health”) could be predicted through: a) inconsistency between selected conditions that could be treated and evidence-based practices, b) inconsistency between reported x-ray use and evidence-based guidelines, and c) level of negative attitude regarding vaccination. The Akaike information criterion (AIC) value, within a sequential logistic regression model, was used to measure the adequacy of the fitted models for each theme and combination of themes predicting the dichotomous outcome variable (unorthodox view versus all others)[30]. The AIC statistic was defined by AIC = -2 maximized log likelihood + 2 × the number of parameters in the model. A smaller AIC value indicates that the model is better at predicting outcome. A likelihood-ratio Chi-square test was used to elucidate the significance of any difference between models. Within each model, parameters are represented as odds ratios describing the size of effect of each explanatory variable on the classification of an individual’s view of the conditions treated. Each parameter was given equal weighting and analysis was completed with and without stratification for practitioner location.