The Discriminatory Power (D) is the average probability that the typing system
will assign a different type to two unrelated strains randomly sampled in
the microbial population of a given taxon.
This tool has been created to help calculate this parameter 

Example: a novel typing system was used to type 100 randomly sampled E. coli strains.
Four types were obtained, and to each type the following number of strains was assigned:
Type A: 40 strains
With this data, discriminatory power was calculated and its value was 0.7071 