SOAN 3120 Chapter Notes - Chapter 2: Quartile, Box Plot, Graphing Calculator
19 Sep 2016
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The most common measure of center is the average, or mean. To find the mean of a set of observations, add their values and divide by the number of observations. The (capital greek sigma) is short for add them all up o o. The subscripts on the observations x are just a way of keeping the n observations distinct. The bar over the x indicates the mean of all the x-values, pronounced x-bar. The mean is not a resistant measure of center: meaning it cannot resist the influence of extreme observations, such as an outlier. The median is the formal version of the midpoint of a distribution, the number such that half the observations are smaller and the other half are larger. To find the median of a distribution: arrange all observations in order of size, from smallest to largest. If the number of observations n is odd, the median m is the center observation in the ordered list.
