Most people in the US think riding in a car without a seatbelt is reckless, to the point that it should be prohibited by law — not to speak of activities like bicycling without a helmet, skydiving, skateboarding on busy streets, and so on.
The WHO’s Burden of Disease Report from December 2004 gives death rates for various causes for various countries. Some selected data:
W149 III A Unintentional Injuries: USA: 36.6; Argentina: 33.8
W150 III A 1 Road traffic accidents: USA: 15.5; Argentina: 11.5
W157 III B 1 Self-inflicted injuries: USA: 10.3; Argentina: 10.2
W060 II A Malignant neoplasms (cancer): USA: 191.9; Argentina: 157.6
W107 II G 3 Ischaemic heart disease: USA: 176.8; Argentina: 90.3
These are death rates per 100 000 population for 2002. These numbers are affected somewhat by the age distribution of the countries; some of the causes of death are much more prevalent among the old than among the young, such as ischemic heart disease. So they will tend to be very low in countries where more of the population is young, either because people die young or because the birth rate has recently increased a lot (or infant mortality recently decreased a lot). Other causes of death, such as traffic accidents, affect various age groups more evenly, although there is still some variation.
I think the numbers might be more graspable as MTTFs, “mean time to failure”, where “failure” in this case means “death”. If you divide 100 000 person-years by the various causes of death, you get life expectancies from a fantasy world where everyone stays the age they currently are until they die, and are divided into groups only affected by a single cause of death:
W149 III A Unintentional Injuries: USA: 2730; Argentina: 2960
W150 III A 1 Road traffic accidents: USA: 6450; Argentina: 8700
W157 III B 1 Self-inflicted injuries: USA: 9710; Argentina: 9800
W060 II A Malignant neoplasms (cancer): USA: 521; Argentina: 635
W107 II G 3 Ischaemic heart disease: USA: 566; Argentina: 1110
These numbers are interesting for three reasons.
First, they give a sort of ceiling on the possible progress of medical science: we can probably defeat cancer through medical treatments, but eliminating suicide would require a kind of totalitarian mind control, and therefore is not ethically possible. But it seems plausible that we could raise average human life expectancy to several thousand years, merely by curing aging and other diseases.
Second, they provide a reasonable basis for comparing the two countries, risk-wise. Road traffic is slightly less dangerous in Argentina than in the US, despite the crazy driving; perhaps that’s because people take public transit more, or because there’s less traffic on the long-distance highways.
Third, they provide a basis for estimating the life-expectancy cost of various risky activities and the life-expectancy benefits of various prophylactic measures, if we heuristically estimate their effects by adjusting known risks. If something doubles your risk of cancer, then your “cancer life expectancy” falls to about 300 years, modulo age-group differences — which means that it has something very roughly like a one in seven chance of killing you, but your actual remaining life expectancy of 40 years or so will only shrink by five years or so. (Less, really, since cancer risk is somewhat weighted toward your older years anyway.) On the other hand, if it multiplies your risk of cancer by 20 — as heavy smoking does for one particular kind of cancer — it shortens your life expectancy by quite a bit. And what about riding motorcycles?
Well, supposing that motorcycles are five times as deadly as cars (to their riders), they might reduce your “traffic life expectancy” from 6500 years to 1300 years. That risk is more or less evenly distributed over your lifespan, so if you have 50 years left, your risk of dying from the motorcycle would be about one chance in 26, and your life expectancy decreases by about a year.
I still wear a seatbelt, because I don’t really get much benefit from not wearing one. But, as a result of calculations like these, I go ahead and bicycle to places even when I don’t have a bike helmet handy.