Researchers studying the long-term cognitive sequelae of mild traumatic brain injury (mTBI) have produced disparate results. Some studies have shown little to no long-term cognitive effects while others have shown that persistent cognitive sequelae continue to affect a subgroup of patients. Meta-analysis has been used to try to integrate these contrasting results to foster a coherent understanding of the cognitive outcomes following mTBI. However, previous meta-analyses of long-term cognitive sequelae have used studies from a period of mTBI research where methodological rigor has been called into question (Carroll, Cassidy, Holm, Kraus, & Coronado, 2004). Using studies from this period, meta-analysts found little to no effect for long-term cognitive sequelae after mTBI: g = 0.07, d = 0.12 (Binder, Rohling, & Larrabee, 1997), g = 0.11(Frencham, Fox, & Mayberry, 2005), and d = -0.07 (Rohling et al., 2011). The present meta-analysis was conducted to address problems with methodological rigor in the studies used in these previous meta-analyses and address differences in meta-analytic methodology (Pertab, James, & Bigler, 2009). Studies published between January 2003 and August 2010 were rated using the 4-tiered American Academy Neurology (AAN) guidelines for methodological rigor to ensure homogeneity and the methodological rigor of included studies. Seven studies were identified that met criteria for a rating of I or II and five met criteria for the lower ratings of III or IV. When studies of all ratings were combined, a significant effect of g = 0.45 was observed. When only studies rated I and II were combined, a significant effect of g = 0.52 was observed while a significant effect of g = 0.38 was observed when only studies rated III and IV were combined. These effect sizes for long-term cognitive sequelae are much larger than those found in previous meta-analyses. Based on these results, it is likely that methodological rigor and/or heterogeneity amongst included studies can impact meta-analytic effect sizes associated with long-term cognitive sequelae following mTBI. However, analyses did not show that more rigorous studies (i.e., those rated I or II) had significantly higher effect sizes than less rigorous studies (i.e., those rated III or IV), t(10) = .636, p = .845. This non-significant finding may be a result of the analysis being underpowered given the small k. Significant effects for neuropsychological domain were also observed and are reported. Additionally, a conceptual critique of mTBI is made with recommendations for future development of the rating system that Cappa, Conger, and Conger (2011) have put forth for objectively rating the methodological rigor of neuropsychological studies. Concerns are addressed related to the mTBI literature in the areas of mTBI definition, definition of cognitive impairment, problems with the constructs of post-concussion syndrome (PCS) and persistent post-concussion symptoms (PPCS), heterogeneity of outcome measurement, and unaccounted for variables.



College and Department

Family, Home, and Social Sciences; Psychology



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mild traumatic brain injury, concussion, meta-analysis, methodological rigor



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Psychology Commons