Mean

The mean is a descriptive statistic that survey researchers commonly use to characterize the data from their studies. Along with the median and mode, the mean constitutes one of the measures of central tendency—a general term for a set of values or measurements located at or near the middle of the data set. The arithmetic mean is the most commonly used measure of central tendency and is what is commonly referred to as the “average” of the data values. The mean is calculated by taking the sum of the data set and dividing by the number of observations to obtain the arithmetic mean. For example, in a data set containing the values 1, 2, 3, 4, 5, 6, 7, 8, and 9, the arithmetic mean would be calculated by adding up the data values—45 in this instance—and dividing by the number of observations—9 in this instance. In this example, the arithmetic mean is equal to 5.

Since the mean takes into account all of the available data within the data set, the mean is highly influenced by outlying data points (outliers). Thus, the median is often used when a data set has outlying data points that could influence the mean and misrepresent the data set. However, it is possible for the mean and median to be equal, for example, in data sets in which the data are normally distributed. The mean is valid only for interval and ratio and not for ordinal and nominal data.

There are many other types of means that can be calculated, including geometric, weighted, harmonic, and so on. The choice of the most appropriate mean to use depends on the nature of the data available. For instance, a geometric mean is commonly used when the data are interpreted according to their product and not their sum. This would be useful when calculating the average rates of annual return in stock investments, when numbers are reported as multiples of the base number. However, these other types of means typically are not used in survey research as much as the arithmetic mean.