Reverse Causality and Whiplash Injury: Three Recent Reviews
Saturday, January 19, 2013 at 4:42PM 
Dan Murphy, DC—
Private Practice of Chiropractic;
Diplomate American Board of Chiropractic Orthopedist;
Faculty Life Chiropractic College West;
Vice President ICA 2003-2009;
ICA Chiropractor of the Year 2009
INTRODUCTION
Reverse causality refers to a direction of cause-and-effect contrary to a common presumption. Reverse causality is cause and effect in reverse. That is to say the effects precede the cause. The problem is when the assumption is A causes B when the truth may actually be that B causes A.
It is usually stated in published studies, by insurance companies, and by their representatives (lawyers, claims adjusters, IME doctors, etc.) that injured patients who seek compensation (ask for compensation, hire a lawyer, etc.)(A), have worse health outcomes and slower recovery rates (B).
However, such adverse health outcomes do not consider or evaluate the concept of Reverse Causality: “slower recovery (B) leads individuals to claim, seek legal advice, and litigate (A).”
The contemporary leaders in the research pertaining to injury compensation, health outcomes, and Reverse Causality are Natalie Spearing and colleagues from the University of Queensland in Australia. In 2011, they published a study in the journal Injury, titled (1):
- Is compensation “bad for health”?
These authors performed a systematic meta-review on this topic, which constituted the most comprehensive review pertaining to compensation and health outcomes through the publication date. In this study, the authors used 11 studies that met their stringent inclusion criteria and noted that 9 of them were of low quality and suffered from a number of methodological flaws.
The studies presented in this review support these concepts:
• Studies that claim that those suffering from chronic problems following whiplash injury do so in hope of gaining financial compensation have methodological flaws.
• The best methodologically done studies show there is no association between litigation/compensation and recovery from whiplash injury.
• It is wrong to claim that chronic whiplash symptoms are primarily the consequence of litigation and desire for monetary gain.
These authors conclude: “There is a common perception that injury compensation has a negative impact on health status among those with verifiable and non-verifiable injuries, and systematic reviews supporting this thesis have been used to influence policy and practice. However, such reviews are of varying quality and present conflicting conclusions.” The contention that “compensation is ‘bad for health’, should be viewed with caution.”
In June 2012, Natalie Spearing and colleagues published another on-topic study in the journal Pain, titled (2):
- Does injury compensation lead to worse health after whiplash?
In this article, Spearing and colleagues introduce the concept of Reverse Causality Bias in the evaluation of the relationship between compensation and health outcome. They note that Reverse Causality Bias occurs when the results of a study are interpreted to mean that whiplash-injured people who hire lawyers to obtain compensation have worse health recovery outcomes; when in fact it may actually mean that whiplash-injured people with greater injuries, more pain and more disability are the ones who seek lawyers to help them obtain the benefits they need.
The authors note that many believe that compensation after whiplash injury does more harm than good. There is a view that injury compensation leads to worse health, called the “compensation hypothesis.” This view that compensation is harmful has been used as an argument for reductions to compensation benefits, to influence judicial decisions, and to advise people that compensation payments will impede their recovery. After their review of the literature, these authors state:
“There is no clear evidence to support the idea that compensation and its related processes lead to worse health.” Claiming “lawyer involvement leads to worse pain,” could also be interpreted as “worse pain increases the likelihood of lawyer involvement.”
“It is important to ascertain whether statistically significant negative associations between compensation-related factors and health do indeed indicate that exposure to these factors leads to worse health, or whether they simply reflect the likelihood that people in comparatively worse health (eg, pain) are more likely to pursue compensation. Unless the latter possibility is considered, decisions to reduce compensation benefits may inadvertently disadvantage those who are in most need of assistance, which would be an undesirable (and unintended) policy consequence.”
In November 2012, Natalie Spearing and colleagues extended their research on these topics with a study published in the Journal of Clinical Epidemiology, titled (3):
- Research on injury compensation and health outcomes: Ignoring the problem of reverse causality led to a biased conclusion
This study highlights the serious consequences of ignoring Reverse Causality Bias in studies on compensation-related factors and health outcomes. These authors evaluated Reverse Causality using a sophisticated mathematical assessment of compensation claims associated with recovery from neck pain (whiplash) after rear-end collisions.
Of the 503 subjects who agreed to participate in the study, 80% developed neck pain within 7 days of collision (early whiplash). Sixty-five percent of those with early whiplash symptoms became claimants, while 35% of those with early whiplash symptoms were non-claimants. Neck pain at 24 months was selected as the primary health outcome. Neck pain severity was measured using the visual analogue scale (VAS) score (0–100).
These authors state: “Although it is commonly believed that claiming compensation leads to worse recovery, it is also possible that poor recovery may lead to compensation claims—a point that is seldom considered and never addressed empirically.” And “When reverse causality is ignored, claimants appear to have a worse recovery than non-claimants; however, when reverse causality bias is addressed, claiming compensation appears to have a beneficial effect on recovery.”
Reverse Causality must be evaluated to “avert biased policy and judicial decisions that might inadvertently disadvantage people with compensable injuries.” And “Once reverse causality bias is addressed, people who claim compensation appear to experience a better recovery from neck pain at 24 months compared with non-claimants.”
“The results of this study suggest that compensation claiming may not be disadvantageous to injured parties after all and that it may even have a beneficial effect,” because access to financial assistance and/or treatment may “indeed relieve pain and suffering. This is, after all, one of the motivations for compensating people who have sustained an insult to their health.”
“This study serves as a reminder of the dangers of drawing causal interpretations from statistical associations when the causal framework is ambiguous. It establishes, empirically, that reverse causality must be addressed in studies on compensation-related factors and health outcomes.”
SUMMARY
These authors reject the hypothesis that the decision to claim compensation negatively affects recovery. In contrast, they show that people with worse health tend to claim compensation. Policies that restrict access to compensation benefits or legal advice may inadvertently disadvantage people who need financial or legal assistance. In addition, many injured people feel compelled to seek legal counsel because it is their belief that their insurance company is treating them unfairly, hindering them from obtaining the treatment they need to recover.
References
- Spearing NM, Connelly LB, Gargett S, Sterling M; Does injury compensation lead to worse health after whiplash? A systematic review; Pain; June 2012;
Dan Murphy, Whiplash Injury 
