This site describes the Nihans ranking algorithm.

As for the single-criteria stratification methods, the best known is the ABC classification. On this site, another one is presented, the Nihans Index. The Nihans Index is more widely applicable than the ABC classification and allows for slightly higher quality stratification than the ABC method.

In addition to explaining the fundamentals of the Nihans Index, this site also provides a downloadable calculator.
With the Nihans Index you can:

  • 1 - Stratify a set of values by negative criteria, including negative values;
  • 2 - Stratify into ABC classes or as many as you want;
  • 3 - Get directly to the "worst" class called W.