A percentile graph, or cumulative frequency curve, is a display tool used by statisticians to show the progression of occurrences in categorical data. The categories are generally progressive as well. For example, if the categorical theme is age, where each category is a certain age range, the data collected would show the frequency of something occurring in each age range.

Calculate and record the cumulative frequency of each of the categories in your data. For each category, add the frequency of its occurrence to the total sum of the frequencies of every preceding category.

Divide the cumulative frequencies of every category by the total frequency of the entire set of data. This will give you the percentile rank of every category. The total frequency of your data can be found by adding up the frequencies of every category in your data.

## Sciencing Video Vault

Plot the percentile ranks you calculated from the previous step. The āxā axis will be the original categories from your data, while the āyā axis will be labeled with percentages.

Draw a line through all of the plotted points to complete the curve. The curve should start at the percentile of your first category and end at 100 percent at your last category.