Mode, Modal Class, Modal Category

Overview

Mode, modal class and modal category are similar statistics that relate to the ‘most popular’ data point within data-sets.

Mode

If the data that you have collected is numerical, the mode is the element that has the highest frequency.

Example 1.

What is the mode of the following data: 5,4,5,8,9,5,8,6,5?

The mode is 5. This is because ‘5’ occurs the most (4-times) in this collection.

Modal Class

In clinical practice, each measured value often occurs at low frequencies, the mode does not give any useful information. However, the data could be grouped to a number of classes and tabulated into a frequency table. The group that has the highest frequency would be the class modal.

Example 2.

What is the class modal of the following mean arterial pressure (MAP) measurements (mmHg): 66, 67, 68, 68, 69, 70, 71 ,72, ,74,75 ,76, 77, 78, 78, 80, 81, 82, 83, 83, 84, 85?

To identify the modal class we would initially  we group the data (e.g. into 5mmHg intervals groups) and, tabulate them into a frequency table.

Table 1. Frequency table. The MAP values have been categorised into groups with a group interval of 5 mmHg (column 1) and, the frequencies of occurrence tabulated in column 2.

As the class which has the highest frequency is 80-84mmHg group, the modal class is 80-84 mmHg.

If two groups had the joint highest frequencies, then we would say that the series has a bimodal distribution.  The bimodal incidence is seen with craniopharyngiomas ( in the 5-14 year and 65-74 year groups) as well as with Sonic Hedgehog (SHH) type medulloblastomas  (< 4 yeas and > 16 years).

The middle value of a modal class can be reported as the mode. In the above example where the modal class was the 80-84 years group, the mode could be reported as 82 – as this is the middle value of the group is 82.

Modal Category

If the data is categorical, then we would use modal category to describe the category with the highest frequency. In the shoe industry, the most popular shoe size for men is size 8. Therefore, the modal category for shoes for men is size 8. With categorical data, modal category is one of the most useful statistics.

Conclusion

Mode, Modal class and modal category are important statistics that inform us which data-point is the most ‘popular’ i.e. has the highest frequency. It is a very informative statistic.