85% Reduction in Injuries and 88% Reduction in Head Injuries

LTRs know that the above title is a paraphrase from a paper I despise:

A case-control study of the effectiveness of bicycle safety helmets by Thompson, Rivara & Thompson. New England Journal of Medicine 1989, Vol 320 No 21 p1361-7.

This is the single most cited paper in all the public agencies in the United States.

I personally think that the Thompson paper is either garbage or highly misrepresented–I’m not smart enough to know which–but I do feel that we need to prove Thompson wrong.

However, Thompson is a peer reviewed paper and that gives it a lot of weight with many people, including me until I looked further into it.

There is a lot of back and forth on whether the famous quotation means what people think it means:

“In regression analyses to control for age, sex, income, education, cycling experience, and the severity of the accident, we found that riders with helmets had an 85 percent reduction in their risk of head injury (odds ratio, 0.15; 95 percent confidence interval, 0.07 to 0.29) and an 88 percent reduction in their risk of brain injury (odds ratio, 0.12; 95 percent confidence interval, 0.04 to 0.40). We conclude that bicycle safety helmets are highly effective in preventing head injury.”

Critics are often called idiots because we don’t understand odds ratio. I don’t know what that means.

But I do know this, I’ll be $1000 to the first person responds that next time there’s a new Mandatory Helmet Law, accounting for the changing population of cyclists, there will NOT be a 88% reduction in brain injury. No weaseling out this time. I don’t care if people wear helmets or not. I’m saying that if there’s a MHL in a state such as California, the next year, there will NOT be 88% less brain injuries in cyclists.

It’s easy to quote papers and call people idiots, and in this case it’s easy for me to make a thousand dollars. Yes, the Unbound household has a budget for extorting fools who believe in this nonsense.

There has been a lot of criticism to this paper. [http://www.cyclehelmets.org/1068.html]

“Numerous studies show that virtually all cyclist deaths and the vast majority of debilitating brain injuries are caused by collisions with motor vehicles. According to one source, not a single helmeted cyclist in the TRT89 study was in collision with a motor vehicle (Snell).”

Plus According to the law (below), the government should do a _comprehensive_ review of the literature. A comprehensive view shows that some studies show a strong safety effect for helmets including MHL, some studies show that helmets are useless, and some show that MHL actually increases risk to cyclists including head injuries.

“With respect to influential scientific information disseminated by the DOT organizations regarding analysis of risks to human health, safety, and the environment, DOT organizations will adopt, with respect to the analysis in question, quality principles of the Safe Drinking Water Act of 1996 (42 U.S.C. 300g-1(b)(3)(A) & (B), except where the agency adapts these principles to fit the needs and character of the analysis. These principles are as follows:

“Use the best available science and supporting studies conducted in accordance with sound and objective scientific practices, including peer-reviewed studies where available.

Use data collected by accepted methods or best available methods (if the reliability of the method and the nature of the decision justifies the use of the data).

In the dissemination of influential scientific information about risks, ensure that the presentation of information is comprehensive, informative, and understandable. In a document made available to the public, specify, to the extent practicable:

Each population addressed by any estimate of applicable effects.

The expected risk or central estimate of risk for the specific populations affected.

Each appropriate upper bound or lower-bound estimate of risk.

Each significant uncertainty identified in the process of the risk assessment and studies that would assist in reducing the uncertainty.

Any additional studies, including peer-reviewed studies, known to the agency that support, are directly relevant to, or fail to support the findings of the assessment and the methodology used to reconcile inconsistencies in the scientific data.”

[http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/subject_areas/statistical_policy_and_research/data_quality_guidelines/html/guidelines.html]

That’s a lot of verbiage. I think that the main point is that the NHTSA and the CDC should give both the lower bound and upper bound percent of people that they expect to be helped by helmets.

So the fact is that even among experts there’s no consensus for whether helmets help at all. A conservative approach, in the lack of any consensus, is to not say anything at all on an issue or to acknowledge the lack of consensus.

Further more, I have been made aware of a list of things that good researchers and public policy organizations do NOT do:

“They do not eagerly seek out the highest possible figures in a series of statistics, independently of their reliability, or otherwise, simply because they want, for whatever reason, to maximize the figure in question, but rather, they assess all the available figures, as impartially as possible, in order to arrive at a number that will withstand the critical scrutiny of others.” [http://en.wikipedia.org/wiki/Denialism]

So even if Thompson had a nice study, over 24 years ago, this single number should not be used to build all of public policy regarding helmets.

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