Nearest rank method
P-th percentile (0 <= P <= 100) of a list of N ordered values (sorted from least to greatest)
is the smallest value in the list such that P percent of the data is less than or equal to that value.
This is obtained by first calculating the ordinal rank,
and then taking the value from the ordered list that corresponds to that rank.
https://en.wikipedia.org/wiki/Percentile
⌈ P ⌉
n = | --- × N |
| 100 |
n: ordinal rank
P: percentile
N: number of elements in list