Campaigns and legislation to encourage the wearing of cycle helmets have not been shown to reduce significant head injuries,[34] and "there is evidence to suggest that some cyclists ride less cautiously when helmeted because they feel more protected".[35] In one experimental study, adults accustomed to wearing helmets cycled more slowly without a helmet, but no difference in helmeted and unhelmeted cycling speed was found for cyclists who do not usually wear helmets.[36] A Spanish study of traffic accidents between 1990 and 1999 found no strong evidence of risk compensation in helmet wearers but concluded that "this possibility cannot be ruled out".[37]