The committee did not find any studies that met the criteria for a primary study of TBI and ALS (see Chapter 4); however, it did identify two secondary studies. Chen and colleagues (2007) found that ever having experienced a TBI was not significantly associated with a higher ALS risk. However, compared with those who did not have TBI, there were significantly higher odds of ALS risk for patients with more than one TBI (OR, 3.1; 95% CI, 1.2–8.1) and patients who had TBI during the preceding 10 years (OR, 3.2; 95% CI, 1.0–10.2). For patients with multiple head injuries in the preceding 10 years, the risk of ALS was more than 11-fold. Kurtzke and Beebe (1980) found a higher frequency of intracranial injury in ALS subjects than in controls and stated that “men dying of ALS more often had a history of injury 15 or more years before death than did the controls during the same period.” The secondary studies generally found higher rates of ALS in the head-injured, but no studies that met the criteria of a primary study were identified.