Why do the estimates I got from an online data tool not match the published estimates?

NSDUH collects highly sensitive information from individual respondents, including data on substance use and mental health concerns. To ensure that individual respondents cannot be identified from their responses, NSDUH public-use files (PUFs) have been treated with a number of disclosure-avoidance methods. Single-year estimates from the Data Analysis System (DAS) use PUFs. We use restricted-use data files (RUFs) to produce estimates for the national report. Although multi-year estimates from the DAS also use RUFs, they are based on a subset of the cases rather than the full files. Estimates generated from the PUF, multi-year RUF and single-year RUF data file may not be the same due to disclosure-avoidance methods applied to PUFs and multi-year RUF.

See this recent PUF codebook for more detailed information on the disclosure avoidance methods that are used for PUFs.