Wednesday, March 12, 2008

Risky Business

This is one of those episodic blog entries that delves into some aspect of my personal life. I've often asked if I'm a risk taker, given my alpine mountaineering passion, rock/ice climbing activities, and my travel around the world

Here's the way I think about my life. Let's say there is an activity that results in 100% chance of death (mortality). Let's call that 1 Mort.

Is it possible to skydive without parachute and survive? Highly unlikely, so such an activity is probably .99999 Mort.

How about flying on domestic airlines? Over the past 20 years, the fatalities per plane flight in the US have been 1 in 7 million. This means that if I took a non-stop flight every day, I would average 19,000 years before succumbing to a fatal crash. Even frequent flyers face minimal cumulative risk over their careers. What's my risk? Last year I took 166 non-stop flights which is .0000237 Morts - 23.7 microMorts.

I'm 45 years old, so let's look at the CDC mortality rate data.

All causes of death 3.52 milliMorts
1 Malignant neoplasms .867 milliMorts
2 Diseases of heart .696 milliMorts
3 Accidents (unintentional injuries) .426 milliMorts
4 Intentional self-harm (suicide) .169 milliMorts
5 Chronic liver disease and cirrhosis .151 milliMorts
6 Cerebrovascular diseases .119 milliMorts
7 Human immunodeficiency virus (HIV) disease .115 milliMorts
8 Diabetes mellitus .10 milliMorts
9 Chronic lower respiratory diseases (J40-J47) .056 milliMorts
10 Assault (homicide) .053 milliMorts

The National Safety Council (NSC) publishes an annual summery of fatalities and accident statistics called Injury Facts.

All accidents have a risk of .56 milliMorts , which is very close to the CDC accident data above for 45 year olds of .426 milliMorts

Motor vehicle accidents are .15 milliMorts per year

My life insurance policy prohibits me from from operating a private plane, skydiving and scuba diving. Per my review of the literature

Operating a single engine private aircraft has a risk of .35 milliMorts
Skydiving has a risk of .30 milliMorts
Scuba diving has a risk of .02 milliMorts

Thus, perceived high risk behaviors are just twice as risky as driving in Boston and are half the risk of having a 45 year old heart.

The medical literature suggests that alpine mountaineering causes 1.87 deaths per 1000 climbing days. Last year, I did 5 days of alpine climbing. That's 9.35 milliMorts compared to the baseline all cause rate for 45 year olds of 3.52 milliMorts

The bottom line is that my highest risk behavior is just 2.65 times more risky than breathing as a 45 year old.

Thus, for the moment, I'll continue to climb, fly commercial aircraft, and do a few alpine ascents every year. At 9.35 milliMorts per year, I've got 107 years to go before I reach a Mort!


Mark Turuk said...

The no-scuba-diving would be a deal-breaker for me, I'm afraid. :-) But to each their own.



Unknown said...

Hi Dr. H,

I strongly support your not-actually-all-that-risky lifestyle. Since you clearly enjoy the alpine ice climbing, the benefits are worth the minimal raises in risk. I would bet you are taking a higher risk working in a hospital than going ice climbing. However, I recommend revisiting some of your statistics calculations.

It seems to compute your expected value for the number of years until flight fatality, you simply figured it would be on your 7th million flight. But each flight is a Bernoulli trial (analogous to a weighted coin flip) so you must take into account the randomness of the distribution. By my calculations, the expected years until a flight fatality is closer to 13,500 rather than your computed 19,000. (I used a negative exponential distribution which derives from an Erlang order 1 equation.) I think your Mort calculations also succumb to the same problem.

I'd be happy to show you my excel spreadsheet. A quick Googling of Bernoulli trials, Poisson distributions and the Erlang equation would be useful background for these kinds of calculations.

Your main point is still valid, though, even if your numbers are a tad off.

Great blog.

Bob R.

John Halamka said...

Thanks Bob!

Here's another correction from my climbing partner, Rick Boyce:

I did a quick estimation of your increased risk of cancer from
exposure to ionizing radiation during air travel. For 166 flights of 3
hrs this gives you around 1 in 10,000 increased risk of cancer per year,
or 100 uMorts. So the cancer risk is about 4X the crash risk.

Unknown said...

Well, it turns out that I did the statistics wrong. I confused discrete with continuous. Your method is indeed sound.

Sorry about that! My bad. Feel free to delete these posts.


Jon said...

interest way of thinking about life! but one question though... all of your calculations consider each event separately. Since hiking is your most "dangerous" activity, isn't the real question what is the mort rate of the all alpine hikers who also have a 45 year old heart?