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Edited on Sat Oct-24-09 11:09 AM by Jim__
I'd say probability is very reliable, statistics, depending on what you're looking for, is more difficult.
Probability is about predicting sample populations from a known population. A simple example of a probability problem, if you have a box containing 30 red balls, 20 green balls and 50 yellow balls, and you randomly select 10 balls from this population, what is the probability that your sample will contain 3 red, 2 green and 5 white balls. A computation of the probability will usually come very close to an actual count from a large number of tests.
Statistics is about going the other way. Same example, given that you have picked 10 balls from a box containing a mixture of 100 red, green, and yellow balls, and you picked 3 red, 2 green, and 5 yellow, what is the probabilty that the percentage of red, green and blue balls is 30%, 20%, and 50%.
When they sample voters to give estimates of what election results would be if they were held today, that's statisitics.
As to the question about correlations, when I was doing statistics, and I found "curious" correlations, I investigated them to find out what the actual relationship was. For instance if 2 variables had a .35 correlation, how were they actually related. My experience (testing specific types of data) was that there was usually a subset of the data for which these 2 variables were strongly correlated (say above .9). Then, investigatign these subsets could tell you a lot about how your system performed under certain conditiions (the conditions of this particular subset). By checking various weakly correlated pairs, you could learn to predict and react to adverse events, either early, or act to prevent them.
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