Descriptive Statistics > How to Draw a Frequency Distribution Table
Watch the video or read the steps below:
How to Draw a Frequency Distribution Table: Overview
A frequency distribution table is one way you can organize data so that it makes more sense. For example, let’s say you have a list of IQ scores for a gifted classroom in a particular elementary school. The IQ scores are: 118, 123, 124, 125, 127, 128, 129, 130, 130, 133, 136, 138, 141, 142, 149, 150, 154. That list doesn’t tell you much about anything. You could draw a frequency distribution table, which will give a better picture of your data than a simple list.
How to Draw a Frequency Distribution Table: Steps.
Step 1: Figure out how many classes (categories) you need. There are no hard rules about how many classes to pick, but there are a couple of general guidelines:
- Pick between 5 and 20 classes. For the list of IQs above, we picked 5 classes.
- Make sure you have a few items in each category. For example, if you have 20 items, choose 5 classes (4 items per category), not 20 classes (which would give you only 1 item per category).
Note: There is a more mathematical way to choose classes. The formula is log(observations)\ log(2). You would round up the answer to the next integer. For example, log17\log2 = 4.1 will be rounded up to become 5. (Thank you to Ayman Masry for that tip).
Step 2: Subtract the minimum data value from the maximum data value. For example, our IQ list above had a minimum value of 118 and a maximum value of 154, so:
154 – 118 = 36
Step 3: Divide your answer in Step 2 by the number of classes you chose in Step 1.
36 / 5 = 7.2
Step 5: Write down your lowest value for your first minimum data value:
The lowest value is 118
Step 6: Add the class width from Step 4 to Step 5 to get the next lower class limit:
118 + 8 = 126
Step 7: Repeat Step 6 for the other minimum data values (in other words, keep on adding your class width to your minimum data values) until you have created the number of classes you chose in Step 1. We chose 5 classes, so our 5 minimum data values are:
126 (118 + 8)
134 (126 + 8)
142 (134 + 8)
150 (142 + 8)
Step 8: Write down the upper class limits. These are the highest values that can be in the category, so in most cases you can subtract 1 from the class width and add that to the minimum data value. For example:
118 + (8 – 1) = 125
118 – 125
126 – 133
134 – 141
142 – 149
150 – 157
Step 9: Add a second column for the number of items in each class, and label the columns with appropriate headings:
Step 10: Count the number of items in each class, and put the total in the second column. The list of IQ scores are: 118, 123, 124, 125, 127, 128, 129, 130, 130, 133, 136, 138, 141, 142, 149, 150, 154.
That’s How to Draw a Frequency Distribution Table, the easy way!
Like the explanation? Check out our statistics how-to book, with hundreds more step by step solutions, just like this one!
Tip: If you are working with large numbers (like hundreds or thousands), round Step 4 up to a large whole number that’s easy to make into classes, like 100, 1000, or 10,000. Likewise with very small numbers — you may want to round to 0.1, 0.001 or a similar division.
If you prefer an online interactive environment to learn R and statistics, this free R Tutorial by Datacamp is a great way to get started. If you're are somewhat comfortable with R and are interested in going deeper into Statistics, try this Statistics with R track.Comments are now closed for this post. Need help or want to post a correction? Please post a comment on our Facebook page and I'll do my best to help!