...Continued
Now, about that 85% figure, this was from one study. I know of one study that stated various studies had a range of 35% to 85% reduction in head injuries from helmet wearing. The 85% figure can be valid, and represent a population this is different in age, sex, the physical environment, etc., so that another population can also have a valid figure of 35%. Helmets themselves differ over time, and that can figure into the result, as can whether a lot of children are involved (difference in height, weight, speed at accident, involvement with cars or trucks, and fit with children verses adults).
Finally, you discuss the three-fold increase in risk of head injury for a miss-fitted helmet, and assert that this translates into greater than a 100% risk of injury. But remember that the 85% figure (or 35%, from other studies) is the potential reduction. Let’s put it this way. Say that we sample 100 cyclists without helmets who hit their heads after falling off their bicycle. We find out that for 85% of them, the exact area that the head hit, which caused a fractured skull or a brain injury, was an area that would have been covered by the helmet had they been wearing one. That means that those 85 people would have been protected from the effects of that particular fall. We know this from the helmet standards and tests that have been conducted on helmets, and from the history of the particular falls. Now, let’s say that the increased risk from a poorly fitted helmet is 1.96-fold increase in head injury for the individual. That means that the ill-fitted helmet user was about twice as likely, with the helmet, to have a brain injury from this fall. Of those seemingly protected 85 individuals, if any one of them had an ill-fitted helmet, and that individual’s head hit the ground instead of the helmet (helmet slid sideways, or up on the forehead), that individual would have a head injury. Let’s say that out of those potentially “saved” a head injury by wearing a helmet, 45 of them had poorly-fitted helmets. Those 45 individuals had a 1.96 higher chance of head injury than did the 40 individuals with good-fitting helmets.
Inj Prev. 1999 Sep;5(3):194-7.Click here to read Click here to read Links
Fit of bicycle safety helmets and risk of head injuries in children.
Rivara FP, Astley SJ, Clarren SK, Thompson DC, Thompson RS.
Harborview Injury Prevention and Research Center, Seattle, WA 98104, USA.
fpr@u.washington.edu
BACKGROUND: Although bicycle helmets are effective in preventing head and brain injury, some helmeted individuals nevertheless sustain head injury. One of the possible reasons may be poor fit of the helmet on the head. This study was undertaken to examine the relationship between helmet fit and risk of injury. METHODS: 1718 individuals who were helmeted riders in a crash were queried on helmet fit and position. A sample of 28 children 2-14 years of age who sustained a head injury while wearing a bicycle helmet and 98 helmeted individuals of the same age treated in the same hospital emergency departments for injuries other than to the head, underwent anthropometric measurements of helmet fit. Measurements were made of the child's head, the helmet, and on a cast made of the child's head. RESULTS: Individuals whose helmets were reported to fit poorly had a 1.96-fold increased risk of head injury compared with those whose helmets fit well. Children with head injuries had helmets which were significantly wider than their heads compared with children without head injuries. Helmet fit was poorer among males and among younger children. CONCLUSIONS: Poor fit of helmets may be associated with an increased risk of head injury in children, especially in males. Helmets may not be designed to provide optimal protection.
This is about as good as I can do right now. My studies have started again, and I am getting much busier with homework, so except for some fairly short comments, this will be my last long post in a while.
John