Introduction to Quantiles

We want to find a solution tt to the problem:

F(t)pF(t)\geq p

to answer questions like "for which income do I belong to the richest 25%?"

How can we calculate this value?

Let FF be a CDF. From Analysis we know that:

  • If FF is continous and strictly monotonic then F(x)=pF(x)=p has F1(p)F^{-1}(p) as solution
  • If FF is only continous then the solution is a nonempty compact interval (more than one solution)
  • If FF does not attain value pp then there is a jump above it

Convergence of quantiles and qq plots

Let FF be a CDF which is the limit of a sequence of ECDFS.

  • If FF has exactly one p-quantile then the smallest and largest quantiles of the sequence of ECDFs converge to this p-quantile
  • Every Accumulation Point of the smallest and largest quantiles of the sequence of CDFs is a p-quantile of FF

Simple tests for distribution equality: