STA 309 Chapter Notes - Chapter 7: Probability Distribution, Probability Plot, Unimodality
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7. 1 the standard deviation as a ruler: z-score = (x mean) / standard deviation. 65 95 99. 7 rule (in a unimodal, symmetric distribution: 68% of values fall within one sd of mean, 95% of values fall within two sd of mean, 99. 7% of values fall within three sd of mean. It"s a continuous random variable; takes on any value: probability density function (pdf) shows distribution of continuous random variable. Gives probability as area below a curve in an interval. I. e. area b/t points -1 and 1 in normal curve is about 68% because of 1 sd from mean. 7. 3 normal probability plots: normal probability plot if the distribution of the data is roughly normal, the plot is roughly a diagonal straight line. Deviations from a straight line indicate that the distribution is not normal. 7. 4 the distribution of sums of normals. 7. 5 the normal approximation for the binomial: success of approximation depends on sample size.
