A frequency table tells you how many items from a data set are in each category.
Within a frequency table:
- The mode is just the category with the most entries
- The range is just the difference between the highest and lowest categories
- The median is the category that contains the middle value of the second column
- To find the mean you add a third column that is the first two multiplied together like this:
The mean = total of third column / total of second column
Grouped Frequency Tables
These are slightly harder. Each category has a class of data rather than just one value.
This means you can only guess the mean…to do so you need to make a 3rd column with the mid-interval values of each class and then a 4th column showing “frequency x mid-interval value”.To estimate the mean divide the total of the 4th column by the total of the 2nd.
Mean = (20 + 84 + 72 + 34) / (10 + 12 + 6 + 2) = 7
NOTE: If in the exam mode or mean come up in reference to a grouped frequency table, you will only be asked to find the modal class or median class, not the exact value.
So for the table above the modal class would be “5 to 9”.