Modal class

Indian Economy glossary

Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 5 "Measures of Central Tendency"

Meaning

The modal class is the class with the highest frequency in a grouped frequency distribution. The mode lies inside this class. The exact mode is then worked out with this formula:

Mo = L + [D₁/(D₁ + D₂)] × h

Here L is the lower limit of the modal class. D₁ is its frequency minus the frequency of the class before it. D₂ is its frequency minus the frequency of the class after it. h is the class width. The formula works only if all classes have equal widths and are exclusive, meaning each upper limit is the next class's lower limit (10-20, 20-30 …). Inclusive classes must be adjusted first.

Example

In NCERT's marks distribution for 100 students, the 50-60 class has the highest frequency, 23. So 50-60 is the modal class, and the mode lies between 50 and 60 marks.

Don't confuse with

  • Mode: the modal class is a range of values. The mode is the single value worked out inside that range.

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