... Other less systematic reports support this finding and suggest that assaults are a more common cause of head injury in lower socioeconomic strata, while sports-related injuries figure more prominently in upper income groups. Head injuries due to assaults and motor vehicle accidents occur most frequently on weekend nights. Occupational hazards for laborers and craftsmen yield a higher incidence of head injury than is noted in business and clerical workers.
Other risk factors for head injury include substance abuse, divorce, preexisting psychiatric disorder, and preexisting head injury. Annegers found that the incidence of head injury is three times higher after a previous head injury and eight times higher after a second head injury (1980).