Clear, well-defined reference value lists which convey information with precision and clarity are essential to unambiguous communication, integration, and interoperability. Members of the PPDM Association expend considerable energy and attention to identifying and resolving key areas where current reference lists are conflicting or
unclear. Well status and classification reference lists used today usually combine many kinds of information in one list, to the extent that one value in a list may explicitly convey more than one kind of information in a complex code, imply (but not state) critical information, or even leave important information out entirely.