Learning how EXACT, TIGHT, MEDIUM and LOOSE settings work on Merge/Purge Plus ALGSEL parameters

It was requested for detailed specific information about how EXACT, TIGHT, MEDIUM and LOOSE settings work on ALGSEL parameters in relation to the input data.

We do not release the proprietary information about exactly how we determine matches.  The Merge/Purge Plus User's Guide does say-

You may tighten or loosen these algorithms individually, as well as introduce special restrictions on the comparisons. Tightening an algorithm means specifying that the records must be closer together to be considered duplicates. By contrast, loosening an algorithm means specifying the elements may be a little more different and still be considered duplicates. By default, all of the algorithms are set for medium matches, but you can tighten and loosen them to meet your needs.
If two records have common elements present, then a sophisticated methodology computes a numeric score based on the similarity of the two  fields. This score is then compared against the minimum allowable score that is represented by the tight/medium/loose setting that you indicated using the appropriate ALGSEL parameter record. If the score is too low to meet the tight, medium, or loose setting you indicated for that element, the two records may be declared unique, or other processing may continue.

For example, in the Merge/Purge Plus program, a setting of medium on the ALGSEL ZIPC parameter record corresponds to a minimum match score of 60. If the computed match score between the ZIP Codes in two records is 59 or less, the records will not be considered as matching ZIP Codes.

And the User's Guide includes a chart of the threshold values for the matching scores required for TIGHT, MEDIUM, and LOOSE settings for the various ALGSEL parameters.
UPDATED:  May 14, 2019