SUMMARY OF E-COURSE: Quantitative Methods Page | 1 Harvar d eCour se1BASICS 1.1Central Values for Data 1.1.1The mean Average = mean = μ (excel: =AVERAGE(value 1 ;value 2 ;…;value n ) far the most commonmeasure used to describe the "center" or "central tendency" of a data set. if the distribution has a tail that extends out to one side —a skewed distribution —the values on that side will pull the mean towards them. 1.1.2The median Excel: =MEDIAN(va lue 1 :value n ) In cases like income, where the data are typically very skewed, the mean often isn't the best value to represent the data. In t hese cases, we can use another central value called the median. The median is the middle value of a data set whose values are arranged in numerical order. Half the values are higher than the median, and half are lower. With an odd number of data points, listed in order, the median is simply the middle value. In a data set with an even number of points, we average the two middle values. The mean weighs the value of every data point, but is sometimes biased by outliers or by a highly skewed distribution. By contrast, the median is not biased by outliers and is often a better value to represent skewed data. 1.1.3The mode Excel: =MODE(val 1 :val n ) to represent the "center" of a data set is its mode: the data set's most frequently occurring value. We might use the mode to represent data when knowing the average value isn't as important as knowing the most common value. In some cases, data may cluster around two or more points that occur especially frequently, giving the histogram more than one peak. A distribution that has two peaks is called a bimodal distribution.
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