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Author: Lurker1999 Big gold star, 5000 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 15265  
Subject: Re: Helmets Put Cyclists At Greater Risk Date: 9/12/2006 9:37 PM
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jammerh writes:
Feel free to ignore this post if you:

1. are not particularly interested

2. (your) mind is closed to considering any new evidence

3. you feel I should shut-up because my opinion doesn't agree with conventional North American thinking on this topic.

4. you feel posters who have a different take on something should remain quiet.


Like walking into an NRA meeting with a gun control T-shirt? Or a bottle of vodka and car keys in hand into a MADD meeting perhaps?

jammerh writes:
Helmeted cyclists take greater risks because they feel helmets offer more protection than they actually do. If this wasn't bad enough in itself, we now know that passing traffic is taking greater risks.

Where was this actually stated in your link? This seems to be your opinion unless you have advance knowledge of the actual article beyond information provided in that link. The way you present the link and then this conclusion is at best misleading and at worst intentional deceit. So before we continue on this line how about a citation or explanation to your statement?

Next let's talk about this journal. The journal is Accident Analysis & Prevention. The link cites: This research has been accepted for publication in Accident Analysis & Prevention, the world's top-rated peer-reviewed ergonomics journal. The journal's actual website (http://www.elsevier.com/wps/find/journaldescription.cws_home/336/description#description) lists the journal's impact factor for 2005 at 1.717. As a comparison the New England Journal of Medicine has an impact factor of 44.016, Science is 30.927 and Nature is 29.273.

So what is a journal's impact factor? http://www.bioreference.net/impact/
Journal Impact Factor is from Journal Citation Report (JCR), a product of Thomson ISI (Institute for Scientific Information). JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. The impact factor is one of these; it is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period.

An impact factor of 1.717 isn't that impressive. There are many flaws with the impact factor system but it's certainly a commonly mentioned piece of information when judging how to rank a journal. Good research gets into better journals "in general." That's why it's better to be published a few times in a good journal than many times in a bad journal.

Let's get to the link itself now. Dr Walker, who was struck by a bus and a truck in the course of the experiment, spent half the time wearing a cycle helmet and half the time bare-headed. He was wearing the helmet both times he was struck.

While it's unfortunate he was hit twice, I don't see how in any context this could lead to statistically significant results where it would affect policy-change on any broad level. At best this could be pilot data for more extensive epidemiologic investigation. Looking at his actual data he was hit by a truck and a bus. The link states that drivers of these types of vehicles passed closer in general. There is no mention in the advance release how this is affected by helmet usage. All I take from the information so far is that drivers of trucks and buses pass closer in general.

However, the advance release also states: Riding position and helmet wearing accounted for 8% of the variance in overtaking proximities.

Without seeing his actual data analysis section I interpret this as an R-squared of 0.08. That means there are another 92% of the variation in distance between vehicles and cyclists that is accounted by other factors. Helmet use is clearly not a huge part of this model.

Before this next part I'll start of by stating I am not an expert in traumatic brain injury epidemiology and how it relates to bicycle helmet use. If you demonstrate somewhat more interest than you have in the past with your other martyrdom posts in actually having a informed and substantiated discussion I'll do a more extensive literature search. In the meantime plugging "traumatic brain injury" and "bicycle helmet" into Google yields the following:

From the CDC: http://www.cdc.gov/od/perfplan/2000/2000xbicycle.htm
Bicycle helmets are a proven intervention that reduce the risk of bicycle-related head injury by about 80 percent, yet bicycle helmets are not worn by most riders.

www.usa.safekids.org/content_documents/ACF160.pdf
A helmet is the simplest, most cost-effective way to prevent wheel-related TBI. Helmets can reduce the risk of brain injury by as much as 88 percent.

This was a UK study. Last time I heard people in the UK were still driving on the left side of the road. There may be problems with generalizability of left sided driving results in this context to the right sided driving patterns in the US.

All the other nitpicking aside, you are at best distorting and at worst deliberating misrepresenting the point of the study in your post. From the advance release overview of the main results (http://www.drianwalker.com/overtaking/) I'll quote: "Motorists might profitably be warned not to make assumptions about a bicyclist's likely experience, or their likely actions during an overtaking manoeuvre, based on their appearance, as in reality gender and helmet-wearing will not be particularly valid signs of experience."

There is no attempt to claim that not wearing a helmet is safer in this link or the advance release. I'll say it again. There is no attempt to claim that not wearing a helmet is safer in this link or the advance release. Why do you think the author did this? Because he knows his study is not powered to affect this type of conclusion. It's only when people like you come along and misinterpret the data that things can go really badly.

jammerh writes:
After a summer of stinging perspiration in the eyes from that wretched piece of yellow styrofoam, and struggling to keep my bike upright while trying to tie the helmet to the bike lock, I'm looking forward to Florida, where a head can breathe.

Listen, you're an adult. Do what you like. If you must have bad data to support your decision-making have at it. But please, make sure that you don't tax the system's resources with care necessary after any type of traumatic brain injury event by ensuring you have plenty of money available in the event that you are involved in an accident.
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