Class Interval

Are you confused between class, class interval, classmark, and class limits in statistics? Look at this page where we are going to explain complete details about Class Interval Statistics. You can learn what is the definition of the class interval, class interval formula, how to calculate the class interval in frequency distribution along with example problems and solutions.

Do Refer:

What is Class Interval in Maths?

Class interval refers to the numerical width of any class in a particular distribution. Mathematically, Class Interval is determined as the difference between the upper-class limit and the lower class limit. In statistics, the data is arranged into different classes and the width of such class is known as a class interval.

Class Interval Formula

The formula to calculate the class interval mathematically is as follows:

Class Interval = Upper Class Limit – Lower Class Limit

Let’s see the below example and understand how class intervals can be found with ease.

Class Interval Example: 

 Class 0 – 5 5 – 10  10 – 15 15 – 20 20 – 25
 Frequency 2 4 0 1 2

Class internal = upper limit − lower limit = 5 − 0 = 5

Similarly, for all classes, 5 – 10, 10 – 15, 15 – 20, 20 – 25.

Class interval = 5 – 10 = 10 – 15 = 15 – 20 = 20 – 25 = 5.

How to find Class Interval in frequency distribution?

A class interval presents the width of each column in a frequency distribution. The following steps help you understand how to calculate class intervals for different frequency distributions:

For instance, let’s consider the following frequency distribution that represents the runs scored by different cricket teams:

Runs Frequency
20-35 4
35-50 3
50-65 2
65-80 1
80-95 2
95-110 0
110-125 1

Step 1: Firstly, take the class interval formula ie., upper-class limit – lower class limit. Here, the lower class limit and upper-class limit are just the smallest and largest possible values in each class.

Step 2: Now, apply the formula and find the class interval for each class. From the above data, the class interval for the first class is 50 – 35 = 15

Step 3: Here 15 is the size of the class interval of the first class. Repeat step 2 for the remaining classes and calculate the size of the class interval for each class in the frequency distribution.

Hence, for the above example, each class interval has a size of 15.

Solved Examples on Class Interval Statistics

Example 1:
What is the frequency of the class interval 30−40?
class interval example
From the given histogram, the frequency of class interval are as follows:
0−10 is 15
10−20 is 10
20−30 is 20
30−40 is 25
40−50 is 10
50−60 is 5.
Hence, the frequency of the class-interval 20−30 is 25.

Example 2:
If the lower and the upper limits of a class interval are 4 and 10, the class interval is _____

The class interval starts from the lower limit and ends at the upper limit.
Hence, Class interval is given by (lower limit − upper limit).
∴ Class-interval for 4 and 10 is 4−10.

Example 3: 
In a frequency distribution with classes (2−9),(10−15),(16−23). What is the class interval?
Class interval = (high − low value +1)
= 9−2+1
= 8.

FAQs on Class Interval

1. What is the size of Class Interval?

The size of the class interval is often selected as 5, 10, 15, or 20, etc.

2. What is Class Interval in grouped data?

The frequency of a class interval in grouped data is the number of data values that come in the range defined by the interval.

3. Define class, class interval, classmark, and class limits in statistics?

In statistics, Class is the subset in which data is grouped, the class interval is the width of that class, classmark is the midpoint of that class, and class limits are upper and lower limits of the class.

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