Which of the following is not a measure of central tendency?

• A. Standard deviation
• B. Mean
• C. Median
• D. Mode

Answer: (A)

Measures of central tendency describe the center of a data set—the value data tend to cluster around. The common ways to express that center are the mean, the median, and the mode. Standard deviation, however, is a measure of dispersion: it tells you how spread out the data are around the center rather than what the center is. The mean is the arithmetic average, the median is the middle value when the data are ordered, and the mode is the most frequently occurring value. For example, with numbers like 1, 2, 2, 3, 100, the mean is about 21.6, the median is 2, and the mode is 2; the standard deviation would be large, indicating wide spread, not the center. Since the question asks for what is not a measure of central tendency, standard deviation is the correct focus.