The mode of a set of data is the value that occurs with the most frequency. The mode is a measure of central tendency, meaning that it is one of a few ways to indicate the center of a data set. Unlike other measures of the center, such as the mean or median, the mode is not necessarily unique.

What if two data values are tied for occurring the most often? In this case our data would have two modes.


To reflect the fact that there is more than just a single mode, we would say that the data set is bimodal.

Example of Bimodal Data Set

We see a bimodal data set in the following:

15, 17, 20, 20, 27, 30, 30, 30, 38, 39, 41, 51, 57, 57, 57, 59, 63, 65, 71, 82

There are a total of 20 data points, and of these data there are 15 different values. The values that occur with the most frequency are 30 and 57. Both of these values occur three times, which is more than any of the other values.  This means that the set is bimodal.

Stem and Leaf

A stem and leaf plot helps to illustrate this bimodal data set:

• 1| 5 7
• 2| 0 0 7
• 3| 0 0 0 8 9
• 4| 1
• 5| 1 7 7 7 9
• 6| 3 5
• 7| 1
• 8| 2

The peaks for both the 30’s and the 50’s illustrate the bimodal nature of these data.