With NACC’s query system, you can determine quickly whether NACC is likely to have subjects you're looking for in numbers sufficient to address your research question. (Also, some research questions about available data can be answered quickly by NACC's data summary tables.) Please note that query results should be used only as rough, preliminary numbers. For publication purposes, please make a custom data request.
Many data elements used in NACC’s direct query system are derived or calculated variables that describe a combination of data elements taken directly from the UDS forms (e.g., “Age at initial visit” is derived from the subject’s birth year and month and the date of the initial UDS visit). The guide to the query system describes the sources for these data elements.