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Comments(3)

An epidemiological examination of the subluxation construct using Hill's criteria of causation

Timothy A Mirtz email, Lon Morgan email, Lawrence H Wyatt email and Leon Greene email

Chiropractic & Osteopathy 2009, 17:13doi:10.1186/1746-1340-17-13

Subluxation, Hill's Criteria of Causation and EBM

James Demetrious   (29 December 2009)  Private Practice email

I read with interest the paper written by Mirtz et al. I have reservations regarding the authors’ conclusions pertaining to the manner in which they have editorialized the subject matter and applied Hill’s Criteria of Causation.

First, I would direct the authors to the paper written by Phillips and Goodman [1] entitled, “The missed lessons of Sir Austin Bradford Hill." Phillips and Goodman report the following:

Making a good decision does not depend on having studies with confidence intervals that exclude the null. A best decision can be based on whatever information we have now, and indeed a decision will be made – after all, the decision to maintain the status quo is still a decision. Hill offered his clearest condemnation of over-emphasizing statistical significance testing, not when he discussed p-values, but when he concluded by saying: "All scientific work is incomplete – whether it be observational or experimental. All scientific work is liable to be upset or modified by advancing knowledge. That does not confer upon us a freedom to ignore the knowledge we already have, or to postpone the action that it appears to demand at a given time."

This would release us from the trap of letting ignorance trump knowledge. Regulators often fail to act because we have not yet statistically "proven" an association between an exposure and a disease, even when there is enough evidence to strongly suspect a causal relationship. There is a growing movement to escape this mistake by making a similar mistake in the other direction: adopting precautionary principles, which typically call for restrictions until we have "proven" lack of causal association – a decision based on ignorance that merely reverses the default. If we can escape from the false dichotomy of "proven vs. not proven," facilitated by the non-existant bright line implied by statistical hypothesis testing and by the notion that causality can be definitively inferred from a list of criteria, then we can make decisions based on what we do know rather than what we don't.

The uncritical repetition of Hill's "causal criteria" is probably counterproductive in promoting sophisticated understanding of causal inference. But a different list of considerations that can be found in his address is worthy of repeating:

• Statistical significance should not be mistaken for evidence of a substantial association.
• Association does not prove causation (other evidence must be considered).
• Precision should not be mistaken for validity (non-random errors exist).
• Evidence (or belief) that there is a causal relationship is not sufficient to suggest action should be taken.
• Uncertainty about whether there is a causal relationship (or even an association) is not sufficient to suggest action should not be taken.

These points may seem obvious when stated so bluntly, but causal inference and health policy decision making would benefit tremendously if they were considered more carefully and more often. The last point may be the most important unlearned lesson in health decision making.

In fairness to those who do not appreciate these points even today, it over-interprets Hill's short paper to claim that he clearly laid out these considerations, or that he was calling for modern decision analysis and uncertainty quantification. But the fundamental concepts were clearly there (and the over-interpretation is not as great as that required to derive a checklist of criteria for determining causation). Several generations of advancement in epidemiology and policy analysis provide much deeper exposition of his points. But Hill still offers timeless insightful analysis about how to interpret our observations. Strangely, these forgotten lessons, which are only slowly and grudgingly being appreciated in modern epidemiology, are hidden in plain sight, in what is possibly the best known paper in the field.

It is my impression that Mirtz et al. have exercised an uncritical repetition of Hill's, "causal criteria," that is counterproductive in promoting a sophisticated understanding of causal inference related to the term, “subluxation.”

I would also caution the authors to carefully apply the tenets of evidence based medicine. Sackett et al. [2] conveyed the following thoughts:

• Evidence based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.
• The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research.
• Good doctors use both individual clinical expertise and the best available external evidence, and neither alone is enough.
• Evidence based medicine is not restricted to randomised trials and meta-analyses. It involves tracking down the best external evidence with which to answer our clinical questions.

Finally, the opinion of Resnick [3] bears consideration: “Evidence-based medicine is a useful tool for summarizing and grading the evidence available in the literature for or against a particular treatment strategy. Its utility is limited by the quality of the primary literature, and the absence of proof cannot be equated with the proof of absence.”

When considering the term, “subluxation,” utilized by the chiropractic profession, it is my impression that stringent adherence to epidemiologic constructs and evidence based medical protocols must not over-shadow clinical experience. Authors must integrate clinical experience and the best available external evidence.

References

1. Phillips CV, Goodman KJ: The missed lessons of Sir Austin Bradford Hill.Epidemiologic Perspectives & Innovations 2004, 1:3.

2. Sackett DL, Rosenberg WMC, Gray JAM, Haynes RB, Richardson WS: Evidence based medicine: what it is and what it isn't: It's about integrating individual clinical expertise and the best external evidence.British Medical Journal 1996, 312(7023): 71-72.

3. Resnick DK: Evidence based spine surgery.Spine 2007, 32(11): S15-S19.

James Demetrious, DC, FACO
Wilmington, NC

Competing interests

No competing interest exists with regard to my professional judgment about the referenced paper that could possibly be influenced by considerations other than the paper's validity or importance.

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Literature support for subluxation theory

John Hart   (05 January 2010)  self email

Editor:

The article by Mirtz et al regarding the application of Hill’s criteria to test whether or not subluxation is causal (1) is interesting but has a few problems, as follows.

1. Hill seems to apply his criteria to association first, rather than causation. (2) Indeed Hill himself warns that criteria alone do not establish cause-and-effect relationships. (2-3)

2. The authors seem to have overlooked literature that could qualify for at least some of Hill’s criteria for association. For example:

a) Given the large percentage of chiropractors (75%) who find that adjustment of subluxation results in improved health of the patient, (4) the criterion of consistency would seem to be satisfied.

b) Given the literature on patients who report improvement after, not before, adjustment of subluxation, i.e., references 5-14 below, the criterion of temporality would seem to be satisfied.

c) Given the literature that proffers plausible theories supporting subluxation theory, i.e., references 15-19 below, the criterion of plausibility would seem to be satisfied.

3. The authors missed an opportunity to point out what it would take to satisfy Hill’s criteria. For example, would they recommend clinical studies, or case reports, or literature reviews, or all of the above? Some of these approaches have already been accomplished regarding the subluxation model, though additional research should be ongoing and would certainly strengthen the model.

4. The authors conclude that the “subluxation construct has no valid clinical applicability” yet they fail to provide hard data to support such a conclusion, apparently basing their conclusion on their lack of findings in the literature. The authors seem to have ignored the axiom that absence of evidence is not necessarily evidence of absence. (20-21)

John Hart, DC, MHSc
Assistant Director of Research
Sherman College of Chiropractic
P.O. Box 1452
Spartanburg, S.C. 29304
USA

References

1. Mirtz TA, Morgan L, Wyatt LH, Greene L. An epidemiological examination of the subluxation construct using Hill's criteria of causation. Chiropractic and Osteopathy 2009 Dec 2; 17:13.

2. Hill AB. The environment and disease: association or causation? Proceedings of the Royal Society of Medicine 1965; 58:295-300.

3. Doll R. Sir Austin Bradford Hill and the progress of medical science. British Medical Journal 1992; 305:1521-1526.

4. McDonald WP, Durkin KF, Pfefer M. How chiropractors think and practice. The survey of North American chiropractors. Seminars in Integrative Medicine 2004; 2(3):92-98.

5. Alcantara J, Plaugher G, Van Wyngarden DL. Chiropractic care of a patient with vertebral subluxation and Bell's palsy. Journal of Manipulative and Physiological Therapeutics 2003; 26(4):253.

6. Kessinger RC, Boneva DV. Vertigo, tinnitus, and hearing loss in the geriatric patient. Journal of Manipulative and Physiological Therapeutics 2000; 23(5):352-62.

7. Alcantara J, Heschong R, Plaugher G, Alcantara J. Chiropractic management of a patient with subluxations, low back pain and epileptic seizures. Journal of Manipulative and Physiological Therapeutics 1998; 21(6):410-8.

8. Elster E. Upper cervical chiropractic care for a patient with chronic migraine headaches with an appendix summarizing an additional 100 headache cases. Journal of Vertebral Subluxation Research 2003:1-10.

9. Alcantara J, Steiner DM, Plaugher G, Alcantara J. Chiropractic management of a patient with myasthenia gravis and vertebral subluxations. Journal of Manipulative and Physiological Therapeutics 1999; 22(5):333-40.

10. Pistolese RA. Epilepsy and seizure disorders: a review of literature relative to chiropractic care of children. Journal of Manipulative and Physiological Therapeutics 2001; 24(3):199-205.

11. Echeveste A. Chiropractic Care in a Nine Year Old Female with Vertebral Subluxations, Diabetes & Hypothyroidism. Journal of Vertebral Subluxation Research 2008 (Jun 9):1-5.

12. Di Duro JO. Improvement in hearing after chiropractic care: a case series. Chiropractic and Osteopathy 2006; 14:2.

13. Plaugher G, Long CR, Alcantra J, Silveus AD, Wood H, Lotun K, Menke JM, Meeker WC, Rowe SH. Practice-based randomized controlled-comparison clinical trial of chiropractic adjustments and brief massage treatment at sites of subluxation in subjects with essential hypertension: Pilot study. Journal of Manipulative and Physiological Therapeutics 2002; 25(4): 221-239.

14. Bedell L. Successful care of a young female with ADD/ADHD & vertebral subluxation: A Case Study. Journal of Vertebral Subluxation Research 2008 (Jun 23):1-7.

15. Dishman R. Review of the literature supporting a scientific basis for the chiropractic subluxation complex. Journal of Manipulative and Physiological Therapeutics 1985; 8(3):163-174).

16. Marino MJ, Langrell PM. A longitudinal assessment of chiropractic care using a survey of self-rated health wellness & quality of life: A preliminary study. Journal of Vertebral Subluxation Research 1999; 3(2):1-9.

17. Sato A, Swenson RS. Sympathetic nervous system response to mechanical stress of the spinal column in rats. Journal of Manipulative Physiological Therapeutics 1984; 7(3):141-7.

18. Bolton PS. Reflex effects of subluxation: the peripheral nervous system. Journal of Manipulative Physiological Therapeutics 2000; 23(2): 101-103.

19. Budgell BS. Reflex effects of subluxation: the autonomic nervous system. Journal of Manipulative Physiological Therapeutics 2000; 23(2): 104-106.

20. Hartung J, Cottrell JE, Giffin JP. Absence of evidence is not evidence of absence. Anesthesiology 1983; 58:298-300.

21. Altman DG, Bland JM. Absence of evidence is not evidence of absence. British Medical Journal 1995; 311:485.

Competing interests

None declared

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Subluxation, evidence-based medicine and epidemiology. Response to comments made by Drs. Demetrious and Hart

Timothy Mirtz   (07 January 2010)  University of South Dakota email

We wish to thank Drs. James Demetrious and John Hart for their thoughtful Letters to the Editor concerning our recent paper “An epidemiological examination of the subluxation construct using Hill’s criteria of causation”[1].

Dr. Demetrious referred us to the paper by Phillips and Goodman entitled, “The missed lessons of Sir Austin Bradford Hill" [2]. We wish to point out that we specifically used the Phillips reference in our paper under the subheading “Limitations to utilizing Hill's Criteria” (Ref #32). Notwithstanding, Phillips and Goodman’s [2] concerns about “statistical significance” and “precision” are irrelevant in the case of subluxation because we simply have no credible data upon which to perform measures of “statistical significance” or “precision”. In our paper we readily agreed with Phillips and Goodman [2] that belief in “. . . a causal relationship is not sufficient to suggest action should be taken.” Something more than mere belief is needed. Unfortunately, in the case of subluxation, chiropractic has not much more than belief to offer. Furthermore, Phillips and Goodman [2] also noted that “Association does not prove causation (other evidence must be considered)”. We also wish to point out that merely discussing subluxation from anecdotal experience and case studies does not mean that a subluxation was actually encountered.

In essence we believe Dr. Demetrious is pointing to Phillips and Goodman’s [2] specific statement: Regulators often fail to act because we have not yet statistically "proven" an association between an exposure and a disease, even when there is enough evidence to strongly suspect a causal relationship.

Granted, our paper does not delve into or consider health policy formulation. But the fact remains that non-chiropractic policy regulators will eventually make decisions about subluxation based upon the best available scientific evidence. After 114 years of chiropractors making claims about the significance of subluxation as a causal factor for sub-optimal health and disease formation there has not been produced sufficient evidence to substantiate such bold claims.

The extant evidence is insufficient to strongly suspect a causal relationship between subluxation and disease and consequently to even go further into the realm of statistical significance seems unnecessary. In other words, the latter portion of the Phillips and Goodman [2] statement has not been met by the chiropractic profession.

We predict that our review will produce fear and apprehension by chiropractors. We also believe that chiropractors who are disenchanted with our findings will be calling upon Phillips and Goodman’s [2] work as “evidence” that there is a subluxation cause and effect association.

Dr. Hart believes that we somehow overlooked literature that would qualify for some of Hill’s criteria. Dr. Hart would like us to believe that the results of a survey of chiropractors (who believe in the subluxation construct) is sufficient evidence to conclude that subluxation can meet the consistency criteria. We respectfully refer Dr. Hart to our paper [1] that stated: For the chiropractic subluxation to meet these criteria it (subluxation) would have to be found repeatedly in different persons, places, times, and circumstances. In the case of a clinical condition, the subluxation would have to be consistently found with the clinical condition. To date there has not been a study that has found the subluxation in any one population (gender, race, ethnicity, age).

The study that Dr. Hart refers to [3] does not satisfy that there is a positive health outcome consistent with any variable such as gender, race, ethnicity or age. Thus the study [3] that Dr. Hart alludes to does not qualify as meeting the consistency criteria.

Dr. Hart also believes that given the literature on patients who report improvement after, not before, adjustment of subluxation that the criterion of temporality would seem to be satisfied. Dr. Hart cites references he believes meet the temporality criterion. For temporality to be met the subluxation must always precede the clinical condition for a true cause and effect scenario to take place. For example, Dr. Hart lists studies that are suggestive that subluxation is found in Bell's palsy, myasthenia gravis vertigo and tinnitus, diabetes, epilepsy and ADHD along with others from his list of references. These studies did not find the subluxation as causal of these clinical conditions. There are other pathophysiological processes that can easily be explanatory. These conditions have other, more scientifically-derived, etiologies.

It is worth noting that most manual medicine practitioners could deliver spinal manipulation to such a case without having to acknowledge that a subluxation was present or not. We find it interesting that only some chiropractors can find a subluxation associated with such pathological states whereas other chiropractors and health professionals do not. Furthermore, what Dr. Hart has provided are merely case studies which in the evidence hierarchy sits low on the spectrum of evidence. Case studies are merely capable of generating an hypothesis and do not prove causation or cure.

Dr. Hart believes that the subluxation model adequately satisfies the biological plausibility criterion. The biological plausibility criterion asks the question “does a pathophysiologic model of how the exposure could cause the disease make sense?” [1] In other words, does the subluxation as a pathophysiologic model of having a subluxation being a causal factor of disease make sense? We suggest that it does not make sense. Nansel and Szlazak [4] noted: it is extremely important to keep in mind that all of the "somato-visceral disease" theories and models put forth over the years, regardless of their lack of biological tenability, have also suffered from a common central premise, that is, that the patients involved in these rather "miraculous" clinical situations were really suffering from true visceral disease in the first place!

Nansel and Szlazak [4] noted: we are aware of not a single appropriately controlled study that has convincingly established that spinal manipulation represents a valid curative strategy for the treatment of any true visceral disease, even though scientifically unsubstantiated claims of such therapeutic efficacy continue to be all too prevalent throughout the chiropractic profession.

After 14 years since this seminal paper was published, we do not know of any study that has established spinal manipulation as a valid curative strategy. We do know that unsubstantiated claims of therapeutic efficacy continue to plague the chiropractic profession. It is our opinion that the ACC Paradigm [5] still lends itself to such claims of therapeutic efficacy in their own definition of a subluxation.

Furthermore, we believe that the non-biological plausibility of the subluxation, seen in the ACC Paradigm, is further explained by Nansel and Slazek [4]. They suggested that: there is not the slightest suggestion that patients suffering from severe, primary, mechanical low back pain, for instance, are more prone to develop higher incidences of prostate or testicular carcinoma, colitis, ovarian cysts, endometriosis, pancreatitis, appendicitis, diabetes mellitus or any other category of regionally or segmentally related organ disease.

We believe that this explanation alone is suggestive of the folly of the subluxation as a biologically plausible explanation as described by the ACC Paradigm [5]. Thus, the biological plausibility is unfounded. What Dr. Hart has brought forward are individual aspects (the five components of the subluxation i.e. kinesiopathology, neuropathology, etc) and suggests that each of these are somehow biologically plausible. By themselves, we agree that they have a level of biological plausibility. However, for a subluxation to be a true entity it should consist of all five components. And this is where the model, in our opinion, falls apart. There simply is no evidence whatsoever suggestive of this subluxation construct. In addition, the mentioning of the five components of subluxation yet detailing only part of the components does not make a subluxation. In summary, the notional entity known as subluxation (for it to be a subluxation) should have all the five components available. Furthermore, such an entity would have to meet cause and effect criteria to be a putative clinical entity worthy of intervention. Our review found no evidence of this.

Dr. Hart laments that we missed an opportunity to point out what it would take to adequately satisfy the criteria of causation. The purpose of this examination was to review the current evidence on the epidemiology of the subluxation construct and to evaluate the subluxation by applying epidemiologic criteria for its significance as a causal factor [1]. Thus our purpose was not in research design or methodology of examining the subluxation. We leave it to the subluxation advocates to address this.

As well, we must point out that we did not intentionally avoid the EBM principles in our paper. The purpose of the paper was to examine the subluxation construct using criteria of causation i.e. Hill’s Criteria. Dr. Demetrious should know that the EBM paradigm was developed by epidemiologists. A thorough reading of Sackett’s work [6] specifically notes the value of epidemiological principles.

However, Dr. Demetrious correctly noted the thoughts by Sackett et al [6], namely:
• Evidence based medicine is the conscientious, explicit, and judicious use of current best evidence.
• The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence.
• Evidence based medicine is not restricted to randomised trials and meta-analyses. It involves tracking down the best external evidence.

We emphatically agree with these views and believe we are quite familiar with the EBM paradigm. Nonetheless, we specifically point out that every single one of these points involves the use of actual evidence. The whole focus of our paper was to examine the evidence and report the findings. These findings demonstrate an absence of any coherent, credible, objective evidence that will support the subluxation construct as it relates to the ACC Paradigm [5]. Simply put, the evidence is simply not there.

It is true that we concluded that the subluxation construct has no valid clinical applicability as Dr. Hart asserts. However, Dr. Hart suggests that we failed to provide hard data to support such a conclusion. We stand by our conclusion based on the lack of findings in the literature. If the subluxation was a valid clinical entity the literature would bear this out. Thus the only conclusion one can draw is that subluxation is a suspect clinical entity.

As well, Drs. Hart and Demetrious have suggested that we have ignored the axiom that absence of evidence is not necessarily evidence of absence. We believe that this comment has been over-utilized by chiropractors to the point of being cringe-worthy. We also believe it is a shield to cover the chiropractic profession and is used as a measure of our collective lack of evidence. Our paper, although preliminary, is illustrative of the “proof of absence.” The burden of proof rests with the chiropractic profession.

We wish to leave this argument with a quote from Charles Darwin that we feel is appropriate to the subluxation debate: “Ignorance more frequently begets confidence than does knowledge.”

Again, we wish to thank Drs. Hart and Demetrious for taking the time to critique of our work and we look forward to seeing new credible research that explores the theoretical construct that is subluxation.

Timothy Mirtz DC, PhD, CHES, CAPE
Lon Morgan DC, DABCO
Larry Wyatt DC, DACBR
Leon Greene PhD

References

[1] Mirtz TA, Morgan L, Wyatt LH, Greene L. An epidemiological examination of the subluxation construct using Hill's criteria of causation. Chiropractic and Osteopathy 2009; 17:13.

[2] Phillips CV, Goodman KJ. The mixed lessons of Sir Austin Bradford Hill. Epidemiol Perspect Innov 2004;1:1-5.

[3] McDonald WP, Durkin KF, Pfefer M. How chiropractors think and practice. The survey of North American chiropractors. Seminars in Integrative Medicine 2004; 2(3):92-98.

[4] Nansel D, Szlazak M. Somatic dysfunction and the phenomenon of visceral disease simulation: a probable explanation for the apparent effectiveness of somatic therapy in patients presumed to be suffering from true visceral disease. J Manipulative Physiol Ther. 1995;18(6):379-97.

[5] Association of Chiropractic Colleges. A position paper on chiropractic. J Manipulative Physiol Ther 1996;19:634-637.

[6] Sackett, DL. Straus SD, Richardson WS, Rosenberg W, Haynes RB. Evidence-based Medicine: How to Practice and Teach EBM. 2nd Edition. 2000. Churchill-Livingstone. Edinburgh.

Competing interests

The authors declare no competing interests.

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