Research on injury compensation and health outcomes: Ignoring the problem of reverse causality led to a biased conclusion

Journal of Clinical Epidemiology November 2012; Vol. 65; No. 11; pp. 1219-1226 Natalie M. Spearing, Luke B. Connelly, Hong S. Nghiem, Louis Pobereskin BACKGROUND FROM DAN MURPHY Reverse causality refers to a direction of cause-and-effect contrary to a commonpresumption. Reverse causality is cause and effect in reverse. That is to say theeffects precede the cause. The problem is when the assumption is A causes B whenthe truth may actually be that B causes A. It is usually stated in published studies, by insurance companies, and by theirrepresentatives (lawyers, claims adjusters, IME doctors, etc.) that injured patientswho seek compensation (ask for compensation, hire a lawyer, etc.)(A), have worsehealth outcomes and slower recovery rates (B). However, such adverse health outcomes do not consider or evaluate the concept ofReverse Causality: slower recovery (B) leads individuals to claim, seek legaladvice, and litigate (A). In my experience, which is extensive, many injured people feel compelled to seeklegal counsel because it is their belief that their insurance company is treating themunfairly, hindering them from obtaining the treatment they need to recover. KEY POINTS FROM THIS STUDY: 1) This study highlights the serious consequences of ignoring reverse causalitybias in studies on compensation-related factors and health outcomes. 2) These authors evaluated reverse causality using a sophisticated (andingenious) evaluation of compensation claims associated with recovery from neckpain (whiplash) after rear-end collisions. 3) Although it is commonly believed that claiming compensation leads to worserecovery, it is also possible that poor recovery may lead to compensation claims apoint that is seldom considered and never addressed empirically. 4) When reverse causality is ignored, claimants appear to have a worserecovery than nonclaimants; however, when reverse causality bias is addressed,claiming compensation appears to have a beneficial effect on recovery. [Key] 5) Reverse Causality must be evaluated to avert biased policy and judicialdecisions that might inadvertently disadvantage people with compensable injuries. 6) There is a prevailing belief that compensation does more harm than good,and this idea that claimants are worse off influences decisions about injurycompensation laws. 7) An assumed belief is that the lure of compensation prompts individuals toexaggerate subjective symptoms. But, no studies have examined the effect ofcompensation payments per se on health. 8) In assessing injury outcomes, reverse causality must also be consideredbecause the causal relationship between compensation factors and health isambiguous. Claiming compensation, lawyer involvement, and litigation, may leadto slower recovery, but it is also possible that slower recovery leads individuals toclaim, seek legal advice, and litigate. 9) The consequences for statistical inference of ignoring reverse causality biasare potentially serious: if negative associations between compensation-relatedfactors and health status actually reflect worse health among those pursuingcompensation (a rarely considered, but entirely plausible proposition), thendecisions to limit access to compensation benefits may do more harm than good. *This study used a source population of 1,174 adults with injuries arising from arear-end vehicle collision. *Of these, 503 agreed to participate in the study. *80% (403/503) developed neck pain within 7 days of collision (early whiplash). *[This means that 20% (100/503) developed neck pain after 7 days of collision]. *65% of those with early whiplash symptoms became claimants (265/403). *35% of those with early whiplash symptoms were non-claimants (138/403). Variable Claimant Non-claimant Number 265 (65%) 138 (35%) Age (mean) 41 43 Female 71% 62% Married 71% 70% Neck Pain 1 wk post MVC 99% 50% Neck Pain, baseline 41.8 19.5 Neck Pain, 6 months 34.7 4.3 Neck Pain, 1 year 26.6 3.3 Neck Pain, 2 years 15.6 1.9 Headache at Baseline 84% 75% Prior Neck Pain 23% 19% Went to ER 75% 61% Went to GP 84% 75% Car Drivable yes 64% 63% Aware yes 25% 25% Prior Collision(s) 20% 17% Not Working at 6 Months 38% 2% 10) Neck pain at 24 months was selected as the primary health outcome. Neckpain severity was measured using the visual analogue scale (VAS) score (0 – 100).Higher VAS scores indicate worse pain: a score of 100 represents the worst painimaginable and zero represents no pain. 11) The analysis offered by these authors is extremely mathematical. They notethat the standard method used to declare compensation negatively affectsrecovery uses a standard single equation approach. However, to assess reversecausality, a simultaneous equations techniques must be used. When thesimultaneous equations techniques are used, the results tell a different story. 12) The usual approach to analyzing the effect of compensation-related healthfactors using the single equation approach is inappropriate and gives rise tobiased and inconsistent results. 13) These authors reject the hypothesis that the decision to claim compensationnegatively affects recovery. 14) Once reverse causality bias is addressed, people who claim compensationappear to experience a better recovery from neck pain at 24 months compared withnon-claimants. [Key Point] 15) The results of this study suggest that compensation claiming may not bedisadvantageous to injured parties after all and that it may even have a beneficialeffect, because access to financial assistance and/or treatment may indeed relievepain and suffering. This is, after all, one of the motivations for compensating peoplewho have sustained an insult to their health. [Key Point] 16) Neck pain is significantly worse at baseline among claimants compared withnon-claimants, which suggests that claims are more likely to be made by individualswhose initial neck pain is worse. [Key Point] 17) Reverse causality is largely overlooked in studies on compensation-relatedfactors. Yet, this study shows that people with worse health tend to claimcompensation. [Key Point] 18) Policies that restrict access to compensation benefits or legal advice mayinadvertently disadvantage people who need financial or legal assistance. [Key] 19) This study serves as a reminder of the dangers of drawing causalinterpretations from statistical associations when the causal framework isambiguous. It establishes, empirically, that reverse causality must be addressed instudies on compensation-related factors and health outcomes. WHAT IS NEW: POINTS FROM AUTHORS: * Reverse causality bias has never been addressed empirically in studies onthe relationship between compensation factors and health outcomes. In spite ofthis, the results of these studies are consistently interpreted as evidence thatexposure to compensation-related factors is harmful to health outcomes. * This study confirms that reverse causality is an important source of bias incompensation research. * Unless all sources of bias, including reverse causality bias, have beenconvincingly addressed, one cannot draw conclusions about the relationshipbetween injury compensation and health outcomes. * The quality of research in this field must be improved to avert decisions thatwill inadvertently disadvantage people with compensable injuries.