Chapter 13b - CHAPTER 13B Normal Distributions EXAMPLE 13.3 Heights of adults ages 18-24 Men mean 70.0 inches standard deviation 2.8 inches So 68 of men

Chapter 13b - CHAPTER 13B Normal Distributions EXAMPLE 13.3...

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C HAPTER 13 B Normal Distributions
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E XAMPLE 13.3 Heights of adults, ages 18-24 Men mean: 70.0 inches standard deviation: 2.8 inches So… 68% of men are between 67.2 and 72.8 inches 95% of men are between 64.4 and 75.6 inches 99.7% of men are between 61.6 and 78.4 inches 2
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E XAMPLE 13.3 What proportion of men are less than 68 inches tall? ? 68 70 (height values) 0 1 -1 2 -2 3 -3 standard deviations: 70 72.8 67.2 75.6 64.4 78.4 61.6 height values: 3
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S TANDARD S CORES & P ERCENTILES The 68-95-99.7 rule helps us to find the percent of observations that fall within 1, 2, or 3 standard deviations of the mean. How do we find the percent above or below values from our data? We have to rely on the standard score and percentile method. 4
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S TANDARD S CORES Observations expressed in standard deviations above or below the mean of a distribution are called standard scores . They are also called z- scores. The standard score for any observation is 5 deviation standard mean n observatio score standard x z
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S TANDARD S CORE So, a standard score of 1 says that our
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