# Life Expediencies

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After my messages about Rock Star: Supernova, I guess now I can talk about the other reality show I watch, NBC’s “Biggest Loser”, which takes a group a overweight people, and puts them through a regiment of diet & exercise. The winner is the one who loses the most weight. I like it because it’s not just about people doing stupid things for money, but about people working to improve themselves. The last two years, on the first episode, I spotted one woman who I though “Ya’know, when she loses some weight, she’ll be really cute”. Both years, that woman came in second. Last year, I had a particularly large crush on Suzy. I didn’t particular like Matt, who, naturally ended up winning the contest, and started dating Suzy. They are now engaged (or possibly already married)

This year, anyone I liked got kicked off, early, so it’s not as much fun. Anyway, that’s not what I want to talk about.

This week they had a special episode, where they ignored the contestants, and sent the trainers out to high schools, to instruct the students on the dangers of being overweight. One of the things they told the students to motivate them was to point out that their parents have a longer life expectancy then they do.

Now, while this is technically true, it’s not nearly as shocking as it sounds. It just shows the widespread misunderstanding on how life expediencies are calculated.

Consider a group of 100 newborn babies. Let’s say that we know that one of them will die each year, with the last one dying at age 100. Now, at the start of this experiment, the life expectancy for the group is 50 years, because the majority of them will live to be at least 50 year old.

Now, consider the group after 20 years, when 20 members of the group have died. What’s their life expectancy then? Now, it’s 60, because of the remaining 80 people, 40 will die before age 60, and 40 will die afterwards.

Wait another 20 years, and the life expectancy is now 70, because of the remaining 60 forty-year-old people, 30 will die before age 70 and 30 will die afterwards.

Wait 50 years, and now there’s only 10 ninety-year-old people left, and those ten would have a life expectancy of 95.

So, now going back to our students, their parents have a longer life expectancy, because they haven’t died yet, while some of the children may die before reaching their parents age. Now, some of the parents peers would also have died at a young age, but they aren’t being counted in the group “your parents”. It’s much like in my example above, and comparing the group at age 20 to the same group at age 40. The people are still dying at the same rate, but the older group has a higher life expectancy merely because they’ve survive as long as they have.

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