A python implementation of the USA Today Diversity Index, first developed by Phil Meyer and Shawn McIntosh of USA Today in 1990; updated in 2000 by Meyer and Paul Overberg.

diversity.py

#!/usr/bin/env python
"""
A python implementation of the USA Today Diversity Index, first developed by 
Phil Meyer and Shawn McIntosh of USA Today in 1990; updated in 2000 by Meyer
and Paul Overberg.

Source and explanation: http://ire.org/resource-center/tipsheets/3473/
"""

def simple(*categories):
    """
    Calculate a simple diversity index score based on percent from categories.
    
    Returns a score from 0 to 1, representing the likelihood that two people
    chosen at random from the group are different from each other.

    0: No diversity. Everyone is the same.
    1: Perfect diversity. Everyone is different.

    USA Today diversity index:
        Diversity = 1 - ((W^2 + B^2 + AmIndI^2 + A^2 + PI^2) * (H^2 + Non-H^2))

    This is a simplified version of that formula, assuming only one factor
    (race, but not ethnicity, for example).

    >>> round(simple(.8, .2), 2)
    0.32

    """
    return 1 - sum(c**2 for c in categories)