A university needs a unique identifier for an individual. There is a Person Identifier assigned by the university to all individuals on campus, but Person Identifier by itself does not guarantee uniqueness.  5% of the time an individual has two distinct Person Identifiers.  Although business rules exist that help enforce uniqueness, errors happen. For example, Bob might be assigned a Person Identifier for his role as student and then a different identifier for his role as instructor. Social Security Number is a possible choice as a unique id, yet we know it has both legal and data quality issues (e.g. foreign students have a temporary social security number until a permanent one is assigned).

What would you choose as the unique identifier for an individual? Would you find a way to fix the data quality problems inherent in Person Identifier or are there other elements that can be used instead?