Risk analysis and estimation...

I hadn't planned on writing a followup on my risk post, but one comment compelled me to write some more. I hope it isn't too preachy.

J writes:

My girlfriend is a doctor. She deals with an inordinate number of motorcyclists every day, from every walk of life. The actual level of risk appears to be very high from the evidence I've seen.

n the final statement, J is asserting that the risk is very high, and he's also asserting that he's basing his conclusion on evidence. There's also an implicit assertion that his conclusion applies to me.

I believe that is an unsupported assertion, and I'd like to discuss why.

The branch of science that deals with risk analysis is know as epidemiology. To pull a definition from a state website:

"Epidemiology is the study of the occurrence and distribution of illnesses and injuries in human populations."

If you read a research paper that says something like, “smoking increases your chance of lung cancer by 45%“, chances are that the work was done by an epidemiologist.

The reason that we do studies in the first place is that it's well known that drawing conclusions from individual experience is often problematic. The whole point of the scientific method is to approach things in an objective and repeatable manner (which doesn't always happen, but that's another subject).

Just to pick a few of the factors that could invalidate J's conclusion (which I'll restate as “Eric shouldn't ride motorcycles because my girlfriend the doctor see's lots of injured motorcyclists“) (and I should note that I'm not asserting that any of these factors are valid or invalid, just listing what are possible sources of error):

1. The doctor may be filtering based on preconception of motorcyclists being more risky
2. The doctor may be giving a summary that is weighted towards more injuries than actually occur
3. The hospital may get a higher percentage of motorcycle injuries than other hospitals in the area.
4. The motorcyclists in the region may ride more miles than in other regions.
5. The region around the hospital may have a higher percentage of motorcyclists compared to a larger population
6. The average motorcyclist age in the region may be younger
7. The region may have less effective motorcycle safety training programs
8. The region may have motorcycle dealers who focus on selling more powerful motorcycles
9. There may be motorcycle clubs who increase the incidence of risky behavior
10. Law enforcement may not be enforcing against risky behavior.

Because of factors such as these, anecdotal data isn't very useful to draw conclusions from (though it is useful to come up with good research topics). You need a real study that looks at motorcycle injuries, looks at the causes of those injuries, looks at the demographics of the situation, and then does some analysis to identify correlations between risk factors and injuries.

(Aside: Epidemilology is a requirement when you're looking at low-level effects, such as environmental cancer rates, danger from EMF radiation, etc. If not, you can't separate clustering due to random distribution (which is by definition not uniform) from a real effect))

So, once you've done that research, you should have a lot of information saying how much more likely motorcyclists are to be injured or killed based on a number of factors. And then you can apply those risk factors to a specific situation, and come up with an estimate on how risky an activity is compared to a different activity.

The literature isn't great in this area, and more study is needed. Many motorcycle accidents come from the actions of other drivers, but I don't know of a recent good study in that area. On single-vehicle accidents, we have the following:

This study states that on a per-mile basis, a motorcyclist is 3x as likely to be injured, and 16x as likely to be killed. But it also lists some risk factors (look to the study for all of them):

Helmet use among fatally injured motorcyclists below 50 percent

High blood alcohol levels are a major problem among motorcycle operators

Almost two thirds of the fatalities were associated with speeding as an operator contributing factor in the crash

Almost 60 percent of motorcyclist fatalities occur at night

Braking and steering maneuvers possibly contribute for almost 25 percent of the fatalities

Almost one third of the fatally injured operators did not have a proper license

I always wear a helmet. I don't drink before I ride. I rarely ride at night. I'm well trained and understand how to properly brake and steer, and I practice a bunch (or I did when I rode more). I have a proper license.

So I don't have a lot of the risk factors that the accident-involved motorcyclist has, so it's unlikely that the 3x and 16x factors apply to my risk as compared to the general population.

Of course, my risk as a car driver is also lower because of good habits, so the relative factors could be the same, or could even be worse.

So, what's my point in all of this? Well, two things.

The first is that many people make the mistake of assessing risk based upon the overall societal attitude towards a activity and/or anecdotal data (“I knew a guy who...“) rather than any factual basis. If you to to an emergency room with a leg injury, you will get a different response based on whether you say you were skiing or skydiving.

My second point is that it takes a good study to tell you how you can reduce your risk, so being better informed really pays off.

Comments

• Anonymous
  June 22, 2004
  The best way to evaluate risk of a certain vehicle over another is to look at the insurance costs associated with them.
  
  Actuarians spend years in college learning about risk assesments and how to evaluate them. Insurance companies spend millions of dollars to evaluate the risks of certain activities so that they can plan and price their premiums accordingly.
  
  If you apply for insurance, you can tell what kinds of things that the insurance companies consider to be risky by what questions they ask you.
  
  There are typically four different types of insurance for vehicles:
  
  1. Insurance for damage to your vehicle.
  2. Insurance for damage caused by your vehicle to other things.
  3. Insurance for damage to you.
  4. Insurance for damage caused by your vehicle to other people.
  
  In this case you would want to compare number 3 between a motorcycle policy and a policy on say a honda civic or something similar.
  
  

• Anonymous
  June 22, 2004
  Lee,
  
  I thought about bringing up the actuarial angle, but decided not to. But since you did...
  
  Insurance companies are in the business of measuring risks accurately (or, accurately enough that they can make money), but my experience is that there are still societal factors at work. Some insurance companies won't want to insure certain bikes for any price, because they don't want that kind of business. One common reason that they don't want that kind of business is because their actuarial models aren't good enough in that area, and it's not worth it to them to take risk that they don't need to.
  
  But, I agree it is possible to do a comparison between two policies, though that will only show you the relative risk difference of the a large segment of the population (say, Male 40 year old motorcycle riders) rather than personal risk, which is likely to be different.

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  The comment has been removed

• Anonymous
  June 22, 2004
  C# programmer: It's even more complex than that.
  
  I decided to blog about it:
  
  http://blogs.msdn.com/jaybaz_ms/archive/2004/06/22/163045.aspx

• Anonymous
  June 22, 2004
  "I don't think that he is misreading them, I think that most statistics written like that are meant to be misread."
  
  I'm afraid I don't follow. Is there a cause-effect relation or just a correlation between your two sentences? :)
  
  "When they report a statistic like the above on television or in print, the large majority of people (Americans especially) just accept it as fact."
  
  Well, it IS a fact. The problem is that people infer much more than it is actually being said in the claim. This is an education issue similar to the one pointed out by Eric.
  

• Anonymous
  June 22, 2004
  Eric,
  
  One of your eariler posts got me to consider getting a motorcycle, so I spent some time looking for safety statistics. The URL is long gone from my bookmarks, but I found the statistics for various modes of transportation put up by some Australian government agency.
  
  Motorcycle riders have 42 times more fatalities per kilometer than car drivers. Of those, roughly 50 percent drover without a helmet, and roughly 50 percent of crashes were caused by other drivers.
  
  I don't know how those probabilities are correlated, but for the sake of the estimate let's say that they are not.
  
  This leaves us with the rider that always wears a helmet and never makes mistakes. In that case he is still ten times (42/2/2 = ~ 10) more likely to get killed per kilometer traveled than a car driver, simply because of other people's mistakes.
  
  We all have different risk tolerances and different fun/risk ratios. But I'd say that it's a pretty safe assumption that you are more likely to get killed on a bike then in a car.
  
  (Fun fact: riding a bicycle and walking are even more dangerous than riding a motorcycle.)
  
  Dejan

• Anonymous
  June 23, 2004
  C# Programmer,
  
  Eric never stated that riding a motorcycle is more safe than driving a car. He is merely pointing out the fact that alot of motorcycle injuries are byproducts of carelessness (in one form or another) and that there is things you can do to minimize the risk of injury. You can't take the risk out of anything but you can always do what you can to minimize it. Some might say if you want to minimize the risk of motorcycle injury then don't ride them. If you feel that way then please, don't ride them. But life could be pretty boring without a little bit of risk.
  
  Adam

• Anonymous
  June 23, 2004
  "problem is that people infer much more than it is actually being said in the claim"
  
  My point was that statistics like this are presented because they want us to infer more into it.
  
  Take the oft-quoted toothpaste statistic "4 out of 5 dentists prefer..." They want us to infer that 80% of all dentists prefer this brand, even though they aren't saying that directly. (and can't because it isn't true)
  
  Getting back to the motorcycle saftey question though, I think it all comes down to what we consider to be risky, which is usually what we are unfamiliar with.
  
  For example, I have a two-car garage and the torsion spring above the door recently went bad.

• Anonymous
  June 23, 2004
  Sorry, got cut off...
  
  For example, I have a two-car garage and the torsion spring above the door recently went bad.
  
  Everything that I read said that working on the spring myself was a death wish, I should cash in my life insurance now, etc...
  
  Then I found a website that showed you how to do it, and said sure, it's dangerous to do this if you aren't careful, but it is no more dangerous than changing your tire. If you carelessly let your leg go under the axel and then accidently knock your jack over, you'll probably have to amputate. However if you are familiar with what you are doing and are careful about it, it isn't a problem.

• Anonymous
  June 23, 2004
  The comment has been removed

• Anonymous
  June 23, 2004
  The comment has been removed

• Anonymous
  June 24, 2004
  http://objectsharp.com/Blogs/barry/archive/2004/06/24/Risk.aspx
  
  It's good to see that you've followed some of MSF Risk Management Principles. You've calculated your Risk Exposure accurately based on Probabilities (driving during day, owning a license, etc) and Impact and you've also worked to lower your risk by wearing a helmet and not drinking.
  
  Project Management and Motorcylces. Who'd have thunk?
  

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  December 29, 2007
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