Methodological Issues in Longitudinal Research on Cognitive Recovery after Traumatic Brain Injury: Evidence from a Systematic Review

Abstract

Background: Previous research addressing cognitive recovery after traumatic brain injury (TBI) in adults has predominately used cross-sectional methods. This systematic review examines longitudinal research into cognitive recovery in the first 2 years following moderate-to-severe TBI in adults and aims to identify apparent methodological issues with the existing literature.Design: Systematic review of the first 2 years post-trauma.Setting: Data were extracted from three electronic databases and manual searches of published articles until October 2012.Participants: Two hundred and forty-two participants with severe TBI and 281 comparison participants were used to calculate effect sizes.Results: Twenty papers met the selection criteria, with effect sizes computed from four studies. Moderate-to-large effect sizes were initially observed between the TBI and comparison groups on most measures (range: d = 0.2–2.8). Recovery continued in all five cognitive domains over the 2 years post-injury.Conclusions: Results demonstrated that cognitive recovery was continuous throughout the first 2 years following moderate-to-severe TBI. Findings also indicated different rates of recovery for the specific cognitive domains, highlighting the heterogeneous nature of cognitive recovery after TBI. The review highlighted several methodological issues within the limited existing literature; recommendations were developed to improve the evidence base.