At NCHS, confidential data from surveys or other data systems are sometimes referred to as PII (personally identifiable information), restricted data, identifiable data, in-house file data, or confidential data.

PII is generally understood to mean direct identifiers, such as name, address and social security number. The terms restricted, identifiable, in-house, and confidential are generally understood to mean microdata, that is, a compilation of individual records that contain indirect identifiers.

Although there are many informal terms used in reference to confidential information, it is crucial to understand the Office of Management and Budget (OMB) definition of PII and to use it consistently when referencing data that must be protected from disclosure.