Fractiles

Another numerical descriptor for the span of frequency distributions is the fractile. A p-fractile is defined as the x-value of the distribution which includes p*N observations, with 0<p<1 and N being the number of observations. An example may clarify this: the 0.1-fractile of the distribution shown below is 14.6, as it includes 10 % of all observations (starting from the left).

The p-fractile is also called P-percentile, with P=p*100.

There are a few special fractiles which have their own definition:

• 1. quartile = 0.25-fractile
• 2. quartile = 0.5-fractile = median
• 3. quartile = 0.75 fractile