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 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). In my experience, which is extensive, 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. KEY POINTS FROM THIS STUDY: 1) This study highlights the serious consequences of ignoring reverse causality bias in studies on compensation-related factors and health outcomes. 2) These authors evaluated reverse causality using a sophisticated (and ingenious) evaluation of compensation claims associated with recovery from neck pain (whiplash) after rear-end collisions. 3) 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. 4) When reverse causality is ignored, claimants appear to have a worse recovery 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 judicial decisions 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 injury compensation laws. 7) An assumed belief is that the lure of compensation prompts individuals to exaggerate subjective symptoms. But, no studies have examined the effect of compensation payments per se on health. 8) In assessing injury outcomes, reverse causality must also be considered because the causal relationship between compensation factors and health is ambiguous. Claiming compensation, lawyer involvement, and litigation, may lead to slower recovery, but it is also possible that slower recovery leads individuals to claim, seek legal advice, and litigate. 9) The consequences for statistical inference of ignoring reverse causality bias are potentially serious: if negative associations between compensation-related factors and health status actually reflect worse health among those pursuing compensation (a rarely considered, but entirely plausible proposition), then decisions 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 a rear-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). 10) 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). Higher VAS scores indicate worse pain: a score of 100 represents the worst pain imaginable and zero represents no pain. 11) The analysis offered by these authors is extremely mathematical. They note that the standard method used to declare compensation negatively affects recovery uses a standard single equation approach. However, to assess reverse causality, a simultaneous equations techniques must be used. When the simultaneous equations techniques are used, the results tell a different story. 12) The usual approach to analyzing the effect of compensation-related health factors using the single equation approach is inappropriate and gives rise to biased and inconsistent results. 13) These authors reject the hypothesis that the decision to claim compensation negatively affects recovery. 14) 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. [Key Point] 15) 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. [Key Point] 16) Neck pain is significantly worse at baseline among claimants compared with non-claimants, which suggests that claims are more likely to be made by individuals whose initial neck pain is worse. [Key Point] 17) Reverse causality is largely overlooked in studies on compensation-related factors. Yet, this study shows that people with worse health tend to claim compensation. [Key Point] 18) Policies that restrict access to compensation benefits or legal advice may inadvertently disadvantage people who need financial or legal assistance. [Key] 19) 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. WHAT IS NEW: POINTS FROM AUTHORS: * Reverse causality bias has never been addressed empirically in studies on the relationship between compensation factors and health outcomes. In spite of this, the results of these studies are consistently interpreted as evidence that exposure to compensation-related factors is harmful to health outcomes. * This study confirms that reverse causality is an important source of bias in compensation research. * Unless all sources of bias, including reverse causality bias, have been convincingly addressed, one cannot draw conclusions about the relationship between injury compensation and health outcomes. * The quality of research in this field must be improved to avert decisions that will inadvertently disadvantage people with compensable injuries.