Acceptable risk

How much life are you willing to spend?

Let's talk about death. Specifically, let's talk about the risk of dying, and how to decide whether a particular activity is "safe enough" or "too risky".

We all make decisions about risk every day. Every time you decide whether to go skydiving, eat a Caesar salad, or have sex with a stranger, you're making a tradeoff between pleasure and dying. Leaving aside (for now) the question of exactly how likely a particular activity is to kill you, how do you decide how much risk is OK? For example, if going cowtipping has a 1 in 10,000 chance of killing you (angry cows, don't you know), does that mean it's safe?

A good starting point is to look at what an economist would call the expected cost of cowtipping. The basic idea is to figure out, on average, how much a cowtipping excursion will shorten your life. For the sake of argument, let's say that you're 40 years old, and expect to live to age 85. That means that you have 45 years = 16,425 days = 394,200 hours of life left. On average, then, going cowtipping will shorten your life by 1/10,000th of 45 years, which turns out to be about 39 hours, or almost 2 days.

An economist would say that the expected cost of cowtipping is 39 hours of life. Here's how the math breaks down for a variety of risk levels:

Risk of death	Expected life cost
1% (1 in 100)	164 days
.1% (1 in 1,000)	16 days
.01% (1 in 10,000)	39 hours
.0001% (1 in 1,000,000)	24 minutes
.000001% (1 in 100,000,000)	14 seconds

The thing that strikes me about these numbers is how big they are. Even an activity with a 1 in a million chance of killing you is still robbing you of 24 minutes of life. It's not until the chance of death falls to 1 in 100 million that the life cost becomes truly trivial.

So, once you've figured out how much life it'll cost you to eat that Caesar salad, or go home with that hunky number from the bar, or whatever, how do you decide what's acceptable? Obviously, it all ultimately comes down to a judgment call, but here are 2 interesting ways of thinking about the problem:

1. Is activity X riskier than driving?

Driving is frequently cited as an example of a risk that's reasonable to take. So how risky is driving? The short answer is that if you're reasonably safety-conscious (you always wear a seatbelt and don't drive drunk), 1 hour of driving has about a .000022% chance of killing you (about 1 in 4.6 million), at an expected cost of 5 minutes of life.

(Here's the math, for the geeks among you. The 2004 US highway fatality rate was 1.46 per 100 million miles of driving. Assuming an average speed of 30 MPH, that's 43.8 deaths per 100 million hours, or .000044% / hour. We'll divide by 2 because we aren't idiots: for example, 55% of all fatalities weren't wearing seatbelts, even though only 25% of all US motorists don't wear seatbelts.)

If you're OK with doing something that's as dangerous as driving, you should stick to activities whose risk of killing you is no more than 1 in 5 million per hour, or a life cost of 5 minutes per hour. If you're OK with doing something that's 10 times as dangerous as driving, your threshold would be 1 in 500,000 per hour, or a life cost of 50 minutes per hour.

2. How much "coma time" is this activity worth to me?

What does it mean to say that cowtipping has an expected cost of 39 hours of life? On average, every time you go cowtipping, you're shortening your life by 39 hours. One way to think of that is to imagine spending that much time in a coma. Is going cowtipping so much fun that I'd be willing to spend 39 hours in a coma, instead of doing all the other things I could do during that time? Obviously, your answer will depend on your personal preference, but at least as far as sex and BDSM are concerned, I think we can make some general statements:

An activity with a 1 in 10,000,000 chance of killing you will cost you about 2 minutes of "coma time". That's not that much: I think most reasonable people would agree that's an acceptable price to pay.

An activity with a 1 in 10,000 chance of killing you will cost you 39 hours of "coma time". That might possibly be worth it for a very rare, "once in a lifetime" experience, but if you're OK with regularly taking that kind of risk, either your day to day life is pretty lame, or you're having way better sex than I am.

So, a 1 in 10,000,000 risk of death is probably OK, and a 1 in 10,000 risk probably isn't. Beyond that, you'll have to make your own decisions.

[Note to self: remember to pack a calculator in the toy bag]