The frequency distribution is the most common method of presenting statistical data. We’ve all seen these types of charts. They present people in groups by age, income level or educational level for example. The key is that once the distributions are established the information can be used to draw inferences for management decision making purposes. The steps are to establish the classes, tally the number of items in each class and count the totals. Following are the steps to building a frequency distribution:
- Establish Classes – The first step in organizing statistical data into a frequency distribution is to define classes. An example would be the total value of parts and labor on repair orders. The data may be organized into groups where the total value was between $100 and $199 then the second group may be those with a total value of between $200 and $299 and so on. A common practice is for all classes to have the same width.
- Tally the Detail Data into the Classes – This step involves summarizing the data into the classes. In our example using the repair orders above we would count the repair orders that fall into the first class ($100 thru $199), the second class ($200 thru $299) and so on. The result gives us a picture of how many repair orders fall into each class.
- Count the Number in Each Class – Once the count for each class has been tallied the numbers can be posted to the frequency distribution table. The table can also be presented with percentages to be used in the analysis of the information.