Total number of blows to the head is based on self-report using the Brain Injury Screening Questionnaire (BISQ). Participants are asked to record the number of times they have experienced a blow to the head in a variety of situations:

Have you ever experienced a blow to the head in the following situations?

1. Vehicle accident? (ex: MVA, pedestrian accident, motorcycle/ATV crash)
2. Hit by an object? (ex: equipment, falling object)
3. Falling? (ex: down stairs, during a fainting spell, from a high place)
4. Sports/leisure? (ex: sports, biking, skiing, on the playground)
5. Physical abuse/assault? (ex: mugged)
6. Military service? (ex: training, blast injury)
7. Other? Please specify.

This variable is the sum of the number of blows in the 7 situations.

Note on missing items: If missing, this variable is set to 0.

Reference: Dams-O'Connor K, Cantor JB, Brown M, Dijkers MP, Spielman LA, Gordon WA. Screening for Traumatic Brain Injury: Findings and Public Health Implications. Journal of Head Trauma Rehabilitation. 2014; 29(6): 479-489. PubMed PMID: 25370440. PMCID: PMC4985006.