NSRCF data files intended for public-use release underwent extensive disclosure risk review to prevent the identity of any facilities, residents, or persons who participated in the survey from being made known to the public. For unusual characteristics and extreme and potentially recognizable outliers, NCHS used a number of methods such as collapsing categories and top or bottom coding to minimize disclosure risk associated with these data items. Furthermore, NCHS checked to see how prevalent certain respondent attributes were in the universe file, and whether they were clustered by geography or selected major facility characteristics. If a given facility or resident characteristic was relatively uncommon in the universe file or was clustered in a specific geographic location, NCHS deemed there was disclosure risk. NCHS used various methods to perturb the data and then ensured that the perturbation did not affect the estimates.