What is the recommended number of class intervals in the frequency distribution?
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Class interval is a term that is used to denote the numerical width of a class in a frequency distribution. In a grouped frequency distribution, data is arranged in the form of a class. The difference between the upper-class limit and the lower limit gives the class interval. Show
In statistics, there are two types of class intervals, namely exclusive and inclusive class intervals. Based on these, a frequency distribution table can be constructed. In this article, we will learn more about a class interval, its types, formula, graph, and see some examples.
What is Class Interval in Statistics?A class interval is used in a frequency distribution table to organize the data obtained from an experiment systematically. The classes in a frequency distribution are usually mutually exclusive. A histogram can be easily constructed by using class intervals. Definition of Class IntervalA class interval can be defined as the difference between the upper and lower class limit of a frequency distribution table. In other words, it is the width of each class. A grouped frequency distribution can be sorted either on the basis of exclusive or inclusive class intervals. Class Interval ExampleSuppose there is a class given by 11 - 21. 11 will be known as the lower class limit while 21 is the upper limit. The class interval is given by 21 - 11 = 10. Class Interval FormulaTo determine the class interval, the lower limit of the class is subtracted from the upper limit. The class interval formula is given as follows: Class interval = Upper Limit - Lower Limit. Inclusive Class IntervalAn inclusive class interval is created using the inclusive method of sorting data into a frequency distribution table. In such a method, the lower limit of a class does not get repeated in the upper limit of the preceding class. When a frequency distribution is analyzed the inclusive class interval has to be converted to an exclusive class interval. This can be done by subtracting 0.5 from the lower class limit and adding 0.5 to the upper class limit. An example of an inclusive class interval is given below:
Exclusive Class IntervalIn an exclusive class interval, the upper limit of one class is the same as the lower limit of the succeeding class. This method of sorting data ensures continuity between two consecutive classes. The value of the mean, median, and mode will be the same irrespective of whether the frequency distribution table has an inclusive or exclusive class interval. Given below is an example of an exclusive class interval.
Class Interval HistogramA histogram is used for visually representing a continuous frequency distribution table. An exclusive class interval can be directly represented on the histogram. However, an inclusive class interval needs to be first converted to an exclusive class interval before graphically representing it. The x-axis represents the class interval and the y axis represents the corresponding frequency. Suppose a frequency distribution table is given as follows:
The class interval histogram is given below:  Related Articles:
Important Notes on Class Interval
FAQs on Class IntervalWhat is a Class Interval?A class interval can be defined as the size of a class in a grouped frequency distribution. It is the difference between the upper class limit and the lower class limit. What is the Formula for Class Interval?The formula to calculate the class interval is given by subtracting the lower class limit from the upper class limit. Class interval = Upper limit - Lower limit. What are the Types of Class Interval in Statistics?There are two types of class intervals in statistics. These are given as follows:
What is an Inclusive Class Interval?An inclusive class interval is one in which the lower class limit of a class is not repeated in the upper class limit of the preceding class. Example, 0 - 5, 6 - 11, 12 - 17. What is an Exclusive Class Interval?In an exclusive class, the lower limit of one class is the same as the upper limit of the preceding class. Example, 0 - 5, 5 - 10, 10 - 15. How to Convert an Inclusive Class Interval to an Exclusive Interval?An inclusive class interval can be converted to an exclusive interval by subtracting 0.5 from the lower limit and adding 0.5 to the upper limit. Can a Histogram Be Plotted for an inclusive Class Interval?No, a histogram cannot be plotted for an inclusive class interval. This is because it will result in a gap between the bars. Thus, such a class interval has to be converted to an exclusive interval before a histogram can be drawn. What is the ideal number of class intervals in a frequency distribution?Good Class Interval size numbers are multiples of 2, or 5. Generally speaking, interval sizes should be between 10 and 20. Less than 10 results in loss of information about the original data and more than 20 is difficult to comprehend. The Number of Class Intervals should reside somewhere between 5 and 20.
How many class interval are there in the frequency distribution?We usually have 6 to 20 classes of equal length. If the number of scores/events is quite large, we usually have 10 to 20 classes. The number of classes when less than 10 is considered only when the number of scores/values is not too large.
What is the ideal number of class intervals for a frequency distribution or histogram?Typically, no fewer than 5 and no more than 20 class intervals work best for a frequency histogram. Choose the first class interval to include your lowest (smallest value) data and make sure that no overlap exists so that one piece of data does not fall into two class intervals.
How many class intervals does the frequency table have?a. There are 7 class intervals.
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