The Berkeley Wellness Letter: "Always wear a helmet"
From the September, 2010 edition of the Berkeley Wellness Letter:
Always wear a helmet when you ride[a bike]. More than 67,000 cyclists seek emergency care for head injuries each year in the U.S., according to the American College of Emergency Physicians, and head trauma accounts for 75% of cycling fatalities. When used properly, bike helmets are nearly 90% effective in preventing brain injuries. ("22 tips for better cycling")