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Politics : Politics of Energy

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Thomas A Watson

To: koan who wrote (43027)	9/8/2013 4:43:11 PM
From: Bilow	2 Recommendations of 86356

Hi koan; Re: "I know a bit about statistics and standard deviations. ... More than 2 standard deviations is only supposed to happen about once every 500 years." Well I know a lot about statistics. I have a lot of degrees in this area and I use them at work all the time. And I know that you're just plain wrong. I'll go over the rather simple math for you. The cummulative table for the normal variable at 2.0 gives 0.9772, see: en.wikipedia.org Therefore the probability of this happening is 1-0.9772 = 0.0228. And 1/0.0228 = 43.8. So you should see deviations of this sort about once in 44 years or so. Re: "So what is the chance of a 1 in 500 event happening 3 times in the last 6 years!??" The "chance" is quite high because the amount of ice is highly correlated from one year to the next. This is in addition to your "1 in 500 event" being an arithmetic error. There are about 10 billion people on the earth. If I pick one, the chance that they're the richest person on the planet is about 1 in 10 billion. Now what's the chance that they're the richest person on the planet next year? Do you really think they only have a 1 in 10 billion chance of winning that lottery again? Of course not, it's not a lottery, the richest people on the planet are highly correlated from one year to the next. Arctic ice is the same way. If there is low ice this year, then it's likely that there will be low ice next year. Recently we've seen a sequence of years with low ice. This should not be worrisome. During the 1970s we saw a sequence of years with high ice. And there was a sequence of years with low ice during the 1940s. The climate has been doing this for millions of years. -- Carl P.S. It's evident that you do not understand how to compute probabilities from standard deviations. To see a worked example of this type of calculation, work through the sample calculation given in this link for the problem: "Suppose pulse rates of adult females have a normal curve distribution with mean µ =75 and standard deviation s = 8. What is the probability that a randomly selected female has a pulse rate greater than 85?" onlinecourses.science.psu.edu You will find that they compute that 85 is 1.25 standard deviations above 75 (i.e. 85 = 75 + 1.25 x 8 ), and then they look up the probability from a table just as I did above. The probability they get (marked with the purple lines) is 0.8944 and so the probability of being larger than this is 1-0.8944 = 0.1056. Hope this helps you with understanding standard deviation.

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