psy 60 winter 2010 ch2 outline

psy 60 winter 2010 ch2 outline - Chapter 2 Describing...

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Chapter 2 Describing Distributions with Numbers Measuring center: the mean “average” value Sigma “add them all up” Not resistant: a few outliers can make s very large. Measuring center: the median “typical” value Median midpoint of a distribution Resistant: outliers do not matter median If # of observations n is odd count (n+1)/2 observations from any sides If # of observations n is even count (n+1)/2 observations then plus then divide by 2 The mean and median of a roughly symmetric distribution are close together. If the distribution is exactly symmetric, the mean and median are exactly the same. In a skewed distribution, the mean is usually father out in the long tail than is the median. Measuring spread: the quartiles First quartile median of the n observations left to the median, larger than 25% of all obs. Second quartile median (larger than 50% of observations) Third quartile median of the n observations right to the median, larger than 75% of all obs. Quartiles are resistant
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psy 60 winter 2010 ch2 outline - Chapter 2 Describing...

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