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Unformatted text preview: ts samples, the laws of probability govern the behavior of the samples. Gallup says that the probability is 95% that an estimate from their sample comes within 3 percentage points of the actual proportion. What does this mean? The Idea of Probability Chance behavior is unpredictable in the short run but has a regular and predictable behavior in the long run. This is the basis of reliance on random samples. If you toss a coin or choose an SRS, the result can't be predicted in advance, but a pattern emerges after many repetitions. Example (10.3) Coin Tossing When we toss a "fair" coin we expect half to be heads and half to be tails. The Count du Buffon (17071788) tossed a coin 4040 times and recorded 2048 heads 2048 for a proportion of = 0.5069 heads. Later (about 1900) Karl Pearson tossed a 4040 12,012 coin 24,000 times and observed 12,012 heads for a proportion of = 0.5005 24,000 heads. As a prisoner of war during WWII, John Kerrich tossed a coin 10,000 times 5067 and got 5067 heads for a proportion of = 0.5067 heads. 10,000 1 M316 Chapter 10 Dr. Berg Here is a plot showing...
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- Fall '08