Follow the procedures below to create a frequency table for a set of quantitative data.

  • Choose a number between 5 and 20 for the number of classes you want to use. You can dial any number. However, this number is likely to increase as a data set grows in size.
  • Calculate the class width using the following formula. Either round the answer up or down to get an appropriate number. The class width determines the size of the classes. The goal is to have classes of the same size. For example, both grades 6-9 and 14-17 have the same width of 4.

Class width =

Highest Score – Lowest Score
/.
Number of classes

  • Pick a number that you will use as the lower bound of the first grade. Choose either the lowest number or a number slightly smaller than the lowest number.
  • Add the class width to the lower bound of the first class to get the lower bound of the second class. Add the class width to the lower bound of the second class to get the lower bound of the third class. Keep doing this until you find the lower bound of the last class. Subtract 1 from the class width. Add the result to the lower bound of the first class to find the upper bound of the first class. To find all other upper bounds, use the same technique as above to find all lower bounds.
  • Find the frequency of each class and put the classes in a table along with the corresponding frequencies.







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