From Grapheme wiki
Percentile filter can be used within Grapheme to filter out data points which have value below a given percentage of observations in a group of observations fall. For example, the 85th percentile is the value (or score) below which 85 percent of the observations belong to. Commonly used percentile values are the 25th percentile - also known as the first quartile, the 50th percentile as the median or second quartile and the 75th percentile as the third quartile.
Computing a Percentile
Unfortunately, there is no standard definition of percentile and several slightly different methods for calculating the percentiles exist. More detailed information can be found here:
To create a Percentile Filter within Grapheme, click on Manage Views icon in the Table Editor toolbar and Edit the Current View. Add a new Percentile Filter, choose the columns that will be used to evaluate the filter and insert the Percentile value, click on OK.