class interval


Class Interval
Definition of Class Interval

While arranging large amount of data (in statistics), they are grouped into different classes to get an idea of the distribution, and the range of such class of data is called the Class Interval.

More about Class Interval

  • Class intervals are generally equal in width and are mutually exclusive.
  • The ends of a class interval are called class limits, and the middle of an interval is called a class mark.
  • Class interval is generally used to draw histogram.

Example of Class Interval

  • In the table above, heights of 20 students of a class are divided into classes with the size of each class interval being 5.

Solved Example on Class Interval

Plant scientists developed different varieties of corns that have a rich content of lysine which is a nutritious animal feed. A group of chicks were given this food to test the quality. Weight gains (in grams) of these chicks after 21 days are as recorded: 380, 321, 366, 356, 349, 337, 399, 384, 410, 329, 350, 340, 324, 396, 412, 420, 382, 318, 344, 438. By constructing a frequency distribution table for 7 classes, find the class interval in which the weight increase is maximum.
Choices:
A. 426 - 443
B. 335 - 351
C. 318 - 438
D. 336 - 353
Correct Answer: D
Solution:
Step 1: Range of the data = higher value - lower value = 438 - 318 = 120
Step 2: Width = Range/number of classes = 120/7 = 17.14 ˜ 18
[Round to the higher value.]
Step 3: Construct the class limits (weight gains) with width 18, so that the least and the highest values are included.
Step 4: The class limits, boundaries, tally marks and the frequency for each class (number of tally marks) are shown in the table.
Step 5:

Step 6: The class interval in which the weight increase maximum is 336 - 353. [Frequency is more for the class 336 - 353.]

Related Terms for Class Interval

  • Histogram
  • Range
  • Subdivision