PDOOMA and error bars

Where the senses fail us, reason must step in.
Galileo Galilei-scientist

For those who do not spend much time studying the charts and graphs attached to articles as diverse as global warming and healthcare, there are often shaded areas on those graphs to indicate the error possibilities; kind of like covering the spread when betting on a basketball game. When things are not an exact science, this is the +/– in percentage, degrees, dollars, etc. These shaded areas are called error bars. I guess one could call it wiggle room for charts, but it is a way of saying they are ‘reasonably’ sure the truth falls somewhere within the error bar limits.

Many charts do not have error bars. This is an indication of one of two things. The numbers either are exact, and not open to question, or they are PDOOMA.

PDOOMA was a new term to me until today. I stumbled over it at Link. Apparently it is a common term among engineers. It stands for Pulled Directly Out Of My Ass. There are other, similar, terms widely in use: WAG (Wild Ass Guess), SWAG (Scientific Wild Ass Guess), Onager Estimate (an Onager is a wild Asian ass), brown numbers, fudge factor and probably hundreds of others of which I have never heard. They all mean the same thing: this chart is bogus; place no credence in it.

This is just a little heads up for your future reading. If you see a chart without error bars on something like the cost estimates for Obamacare, figure it was PDOOMA and could be off by several hundred percent.

Yet, many things like the global warming proxies in Mike Mann’s discredited hockey stick chart do have error bars; and when they do, pay attention to them. If they indicate the error possibility of +/- 2 degrees C or more, when talking about .762 degrees of temperature change, that indicates the .762 degree falls well within the limits of statistical error and has no meaning.

See, this science stuff is getting easier already.

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Published in: on May 17, 2010 at 4:03 pm  Leave a Comment  
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