…This brings to mind another common violation of probability by prime time TV journalists, who may be selected for their looks, charisma and their presentation skills, but certainly not for their incisive minds. For instance, a fallacy that I saw commonly made by a prominent TV financial "expert" is as follows: "The average American is expected to live 73 years. Therefore if you are 68 you can expect to live 5 more years, and should plan accordingly." She went into precise prescriptions of how the person should invest for a 5 more years horizon. Now what if you are 80? Is your life expectancy going to be minus 7 years? What these journalists confuse is the unconditional and conditional life expectancy. At birth, your unconditional life expectancy may be 73 years. But as you advance in age and do not die, your life expectancy increases along with your life. Why? Because the other people dying have taken your spot in the statistics, for expectation means average. So if you are 73 and are in good health, you may still have, say, 9 years in expectation. But the expectation would change, and, at 82, you will have another 5 years, provided, of course you are still alive. Even someone 100 years old still has a positive conditional life expectation. Such a statement, when one thinks about it, is not too different from the one that says: our operation has a mortality rate of 1%. So far we have operated on 99 patients with great success; you are our 100th, hence you have 100% probability of dying on the table.

More Lies, Damned Lies