What are Masked Variance Unites (MVUs) and why do we need them in analyses?
Primary Sampling Units (PSU) are selected from strata defined by geography and proportions of minority populations. Most strata contain two PSUs. Together, these strata and the PSUs represent the variance units (sampling units used to estimate sampling error). To protect the confidentiality of data obtained from sample persons, Masked Variance Units (MVU) are constructed. MVUs are equivalent to Pseudo-PSUs used to estimate sampling errors in past NHANES. The MVUs on the data file are not the “true” design PSUs. They are a collection of secondary sampling units aggregated into groups for the purpose of variance estimation. They produce variance estimates that closely approximate the variances that would have been estimated using the “true” design variables. These MVUs have been created for each two-year cycle of NHANES and have been created in a way that allows them to be used for any combination of data cycles. These MVUs are used to define the strata and PSU variables on the public re
