Vanderploeg and colleagues (2005) used the same cohort to conduct a cross-sectional study of neuropsychologic outcomes. A full 15-measure neuropsychologic battery with neurologic measures of tandem gait and peripheral visual attention was administered. Results revealed no statistically significant difference in any of the measures among the three groups. In examining more subtle differences in attention, concentration, and memory, it was found that the mild-TBI group had significantly higher odds of being unable to continue the Paced Auditory Serial Addition Test (PASAT) than either of the two control groups (comparison with normal control group: OR, 1.32; 95% CI, 1.00–1.73; comparison MVA control, OR, 1.53; 95% CI 1.10–2.13). With respect to working memory, the mild-TBI group had excessive proactive interference (comparison with normal control group: OR, 1.66; 95% CI, 1.11–2.47). PASAT continuation problems were associated with left-side visual imperceptions, and excessive proactive interference was associated with impaired tandem gait in the mild-TBI group.


In another study of the VES cohort, Vanderploeg and colleagues (2003) conducted logistic regression analyses to survey long-term outcomes of work and marital status in people who had mild TBI and any pre-existing factors that may perpetuate the symptoms of the injury. The author notes that the subsample (after exclusion of 53 people because they were hospitalized and 87 because data on them were incomplete) consisted of 4,322 people: 626 (14%) who had a mild TBI (373 without LOC, and 253 with LOC) and 3,896 (86%) who did not have a TBI. Psychiatric disorders were assessed with the Diagnostic Interview Schedule (DIS-II-A), and psychosocial outcomes were gathered by trained examiners. Results indicate that the outcome of a mild TBI may be influenced by the presence of any pre-existing demographic, medical, or psychiatric factors. Factors associated with work and marital status accounted for 23% and 17%, respectively, of the variance in those with head injury. Variance was significantly lower in those without head injury: 13.6% and 9.4%, respectively.

POPULATION-BASED STUDIES

Rochester Epidemiology Project

The Rochester Epidemiology Project is a medical-records-linkage system that encompasses detailed health-care information on residents of the City of Rochester and Olmsted County, Minnesota. Funded initially in 1966 with medical records dating back to 1910, the project was designed to link all medical data and clinical information developed by the Mayo Clinic with data obtained by community health providers, including Olmsted Medical Group, the Olmsted Community Hospital, the University of Minnesota Hospital, and the Minneapolis VA Medical Center. Each patient was assigned a unique identifier, and information on all medical visits has been recorded for each patient. The database includes thorough medical histories, clinical assessments, consultation reports, surgical procedures, laboratory and radiology results, death certificates, and autopsy reports (Flaada et al., 2007). The medical information is continuously updated into an electronic format. By maintaining complete medical histories, the Rochester Epidemiology Project provides the capability to conduct population-based studies of disease risk factors and health outcomes and can be used to study long-term secular trends in disease incidence (Melton, 1996). As of 1996, the project included medical records on a population with more than 3.6 million person-years of experience in 1950–1995 (Melton, 1996). The demographic characteristics of Olmsted County residents largely resemble those of the US white population (Melton, 1996). Over 1,500 publications have resulted from the project,



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