What is the mean of a group of measurements?

• A. The mathematical average of all the measurements
• B. An indication of how similar all the measurements are
• C. The variable that is being measured
• D. The mathematical sum of all the measurements

Answer: (A)

The mean is the central value of a set of measurements. It’s found by adding all the measurements together and then dividing by how many measurements there are, i.e., the mean equals the sum divided by the count. This is the mathematical average that represents where the data cluster around on average.

This differs from other ideas: it isn’t a measure of how similar or varied the measurements are (that would be spread like variance or standard deviation), and it isn’t the actual quantity being measured itself. It also isn’t the total sum, which omits the crucial division by the number of observations. For example, measurements 3, 5, and 7 have a sum of 15; the mean is 15 divided by 3, which equals 5.