Frequency distribution | Statistics

The frequency distribution is a method to organize data within the field of descriptive statistics. A frequency distribution is a grouping of data into mutually exclusive classes with the number of observations in each class.

A frequency distribution is made in the form of a table where the classes are arranged on the left side and the number of observations is entered to the right of the classes. When organizing data in a frequency distribution, you should follow some important steps:

1. How many classes should the raw data be divided into?
We have to use so many classes that we can see the shape of the distribution. A good method to determine how many classes to be selected is the 2^k method, where k is the number of classes. According to the 2^k method, 2^k shall be larger than the number of observations. This method can be used to determine the number of classes.

2. How large class intervals should it be?
All classes should have equal class intervals and thefirst class must cover the minimum value and the last class will cover the highest value in the raw data. The class range can be determined using the formula below.

Class intervals > ((maximum value - minimum value) / number of classes)

Class intervals should be in integers and shall be rounded up if it turns out that the calculated class interval not is an even integer.

3. What should the class boundaries be?
Class limits must be clear so that an observation only can be categorized into one and only one class. Overlapping and unclear class boundaries should be avoided. Class limits may be added as follows, 1000-1999 and 2000-2999, etc.. The first and last class may be open classes, which means that the lowest class may incorporate any value below 999 and the highest class can incorporate all values over 3000.

4. Put all observations in the correct class.
Make one check for each observation, in the class which the observation belongs to.

5. Count the number of checks in each class.
Count the number of checks in each class and type in the number of observations for each class. The number of observations in each class is called the class frequency.
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