Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

A Bit More on the Life Expectancy Chart

Last week, I wrote about the CDC’s latest MMWR (Morbidity and Mortality Weekly Report), which includes a graph of the change in life expectancy from 1970 to 2007. It is broken down by race (black/white) and gender. It shows a continuing increase in life expectancy.

What it also shows is something that confuses a lot of people. Look at the solid blue line – the average life expectancy.

Is the life expectancy of most people better than average (not necessarily a Lake Wobegon effect), average, or worse than average?


http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5651a7.htm

The solid line is the average life expectancy. Most of the lines are below that average.

Let me create a different chart to show the same idea. With financial information, since people seem to be much more concerned with their relative wealth than with most other comparisons. Assume that the numbers 1 to 5 on the chart below are different people. The other numbers (50 and 100) represent the annual income in thousands of dollars of these people – that is 50 = $50,000. We have 5 people with a total of $300,000 annual income. 300/5 = 60 (or $300,000/5 = $60,000). The red horizontal line at 60 in the middle of the chart is at the average (mean average) for these 5 people. These incomes are not unusually high, or low.

Why do so many of us believe that most people in a group cannot be above/below average?

It is not unusual to hear the word impossible used when someone presents data that show that most people can be below/above average.

Is this impossible?

Is this even uncommon?

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Comments

  1. You can’t forget that all the women are strong and all the men are good looking too!

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  2. […] Medics Tue, 21 Sep 2010 08:19:26 +0000 By Rogue Medic Leave a Comment What if the numbers in the chart in my last post did not represent […]