The "basic sampling
weights" are equal to the inverse of the probabilities of selection
of sample respondents. To obtain "final NHSDA weights," the basic
weights were adjusted to take into account dwelling unit-level and
individual-level nonresponse and further adjusted to ensure
consistency with intercensal population projections from the United
States Bureau of the Census.
Data were collected by Research Triangle
Institute, Research Triangle Park, NC, and prepared for release by
National Opinion Research Center, Chicago, IL.
To protect the confidentiality of
respondents, all variables that could be used to identify individuals
have been encrypted or collapsed in the public use file. These
modifications should not affect analytic uses of the public use
Users who wish to replicate results published in the NHSDA
Main Findings Report or other SAMHSA reports should use the 1995 NHSDA
imputed data for prevalence estimates rather than raw data from the
questionnaire or drug answer sheets.
Family and personal income
range variables were constructed from two imputation-revised variables
that were deleted from the public use dataset and codebook due to
confidentiality issues. Users are advised that the recoded income
range variables cannot be replicated from the imputation-revised
variables (IRFINC1 and IRPINC1) contained in the public use file.
For selected variables, statistical imputation was performed following
logical imputation to replace missing responses. These variables are
identified in the codebook as "...LOGICALLY IMPUTED" and
"...imputed" for the logical procedure or by the designation
"IMPUTATION-REVISED" in the variable label when the statistical
procedure was also performed. The names of statistically imputed
variables begin with the letters "IR". For each imputation-revised
variable there is a corresponding imputation indicator variable that
indicates whether a case's value on the variable resulted from an
interview response or was imputed by the hot-deck technique. Hot-deck
imputation is described in the codebook.
For some drugs that have multiple names, questions regarding the use of that drug may be asked for each distinct name. For example, even though methamphetamine, methedrine and desoxyn are the same drug, their use was measured in three separate variables.
Household Survey on Drug Abuse questionnaire and estimation
methodology changed with the implementation of the 1994-B
survey. Therefore, estimates produced from the 1995 survey are not
comparable to those produced from the 1994-A and earlier surveys.