Measures of Central Tendency

The Mean

The mean is the most commonly used measure of central tendency. It is often referred to as x-bar, x, and is found by using the formula, x =

where

xi represents the individual observation from the ith subject;

P is the summation sign that indicates that you sum over everything that follows it. The limits below and above the sign indicate where you start, and stop, the summation, respectively. As it is written above, it says you should begin summing with x1 and stop with xn; and

n represents the number of observations in your data set.

For illustrative purposes, consider the data in Table 1. To compute the mean height, we do the following:

• 1.
  Sum over all the observations (the xi values).
• 2.
  Divide the quantity in Step 1 by the total number of observations. 1

For the data set above, the above formula gives

The Median

The median is used less often than the mean to describe the central tendency of a set of continuous data, but is still a commonly used measure. It is the midpoint of the data, and is often denoted with the letter M: To find the median, the following steps are

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