Let me introduce you to the Levenshtein distance formula. It is awesome:
http://en.wikipedia.org/wiki/Levenshtein_distance
In information theory and computer science, the Levenshtein distance is a string metric for measuring the amount of difference between two sequences. The term edit distance is often used to refer specifically to Levenshtein distance.
Personally I used this in a healthcare setting, where Provider names were checked for duplicates. Using the Levenshtein process, we gave them a confidence rating and allowed them to determine if it was a true duplicate or something unique.