2.2.4. The quantile computation

There are several ways of estimating the quantiles implemented in Uranie. This part describes the most commonly used and starts with a definition of quantile.

A quantile \(x_p\), as discussed in the following parts, for \(p\) a probability going from 0 to 1, is the lowest value of the random variable \(X\) leading to \(P\left\{X \leq x_p \right\} = p\). This definition holds equally if one is dealing with a given probability distribution (leading to a theoretical quantile), or a sample, drawn from a known probability distribution or not (leading to an empirical quantile). In the latter case, the sample is split into two sub-samples: one containing \(pN\) points, the other one containing \((1-p)N\) points.