Octiles for ungrouped data
Octiles are the values of arranged data which divide whole data into eight equal parts. They are 7 in numbers namely $O_1,O_2, \cdots, O_7$. Here $O_1$ is first octile, $O_2$ is second octile, $O_3$ is third octile and so on.
Formula
The formula for $i^{th}$ octile is
$O_i =$ Value of $\bigg(\dfrac{i(N+1)}{8}\bigg)^{th}$ observation, $i=1,2,3,\cdots, 7$
where $N$ is the total number of observations.
