The National Center for Health Statistics (NCHS) developed the Research Data Centers (RDC) to allow researchers access to restricted data. Today, in addition to providing access to NCHS data, the RDC also hosts restricted data from a variety of groups within the Department of Health and Human Services (HHS).
Data are typically classified as restricted if they contain particularly sensitive confidential information about the participants. This might include reports of sexual behavior, criminal history, drug use, mental health history, HIV status, information collected from minors, or other materials that warrant extra discretion. DSDR and its data providers take the confidentiality of these subjects especially seriously. Data held by DSDR never contain direct identifiers, but there is still a risk that participants in these sensitive studies could be identified indirectly. Using a handful of a known participant's demographic characteristics, a person could narrow down the sample significantly and infer which responses belong to the subject they seek. This is called deductive disclosure risk. One way to counteract this risk is by restricting access to the data and carefully reviewing each applicant to ensure that the data are being used strictly for research purposes.