To calculate the risk of a freak accident happening during a single year, you need two numbers: the population in that year and the number of deaths resulting from that type of circumstance during that year. For example: What is the risk of being injured in an amusement park accident?
First we need to know that in 2009 about 280 million Americans visited amusement parks -- this is the park population. Then we need to know that there were 1,086 reported park accidents that year. Divide the number of park guests by the number of reported injuries and you find that American amusement park visitors have about a 1 in 257,826 chance of being injured in a single year.
To calculate the chance of being injured this way in a lifetime, you need to know the one-year chance we just calculated and divide it by the life expectancy of a person born in that year – in this case, 2009. In 2009, American amusement park guests had a 1 in 257,826 chance of being injured at a park. The life expectancy at birth in 2009 was 78.5 years. Divide 257,826 by 78.5, and that makes the lifetime odds of being injured at an amusement park 1 in 3,284 [source: IAAPA, CDC].
Whether or not a freak accident happens to you isn't as black and white as these calculations alone. Look at it this way: Sure, the odds of being in a fatal car accident are greater than being attacked by a shark, but also keep in mind that more Americans ride in cars than swim or surf in shark-dwelling waters. If you live in Wichita, Kan., for example, you're about 1,400 miles (2253 kilometers) away from Venice Beach, Cal. and about 1,400 miles (2253 kilometers) from Venice, Fla. If you travel less than 1,200 miles (1931.2 kilometers) from home during your vacations -- most Americans vacation between about 100 and 1,200 miles (160.9 and 1931.2 kilometers) from home -- your risk of a shark attack, or even ever seeing the ocean for that matter, is going to be lower than a person who surfs in the Red Triangle, a spot off the coast of California that's notorious for sharks and shark injuries. In this instance, your location helps to mitigate your risk.
While you may not be able to foresee all ways to prevent injury or death resulting from an act of nature (or perhaps your neighbor's trampoline), you are in control of lowering your risk of premature death from such things as chronic disease, including heart disease, diabetes and cancer. Quit smoking, exercise at least 30 minutes every day and eat a healthy diet -- and to be safe, never rock or tilt a vending machine to get that stuck candy bar.