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* Description/Instructions. The familiar measures of center (mean, median, mode) and spread (range, standard deviation, variance, and interquartile range) will generally not be directly tested on the AP exam, because you can determine these so easily on your calculator. Description/Instructions. The familiar measures of center (mean, median, mode) and spread (range, standard deviation, variance, and interquartile range) will generally not be directly tested on the AP exam, because you can determine these so easily on your calculator.
Unlike range and quartiles, the variance combines all the values in a data set to produce a measure of spread. The variance (symbolized by S2) and standard deviation (the square root of the variance, symbolized by S) are the most commonly used measures of spread. We know that variance is a measure of how spread out a data set is. It is calculated as the average squared deviation of each number from the mean of a data set. For example, for the numbers 1, 2, and 3 the mean is 2 and the variance is 0.667. [(1 - 2)2 + (2 - 2)2 + (3 - 2)2] Ã· 3 = 0.667.