mental health services,
substance abuse treatment,
Date of Collection:
Unit of Observation:
The civilian, noninstitutionalized population of the
United States aged 12 and older, including residents of
noninstitutional group quarters such as college dormitories, group homes, shelters, rooming houses, and civilians dwelling on military installations.
Data Collection Notes:
Data were collected and prepared for release by
Research Triangle Institute, Research Triangle Park, North Carolina.
Since 1999, the survey sample has employed a 50-State design with an independent, multistage area probability sample for each of the 50 States and the District of Columbia.
Prior to the 2002 survey, this series was titled National
Household Surveys on Drug Abuse.
Although the design of the 2008 survey is similar to the design of the 1999 through 2001 surveys, there are important methodological differences since 2002 that affect the 2008 estimates. Each NSDUH respondent since 2002 has been given an incentive payment of $30. This change resulted in an improvement in the survey response rate. In addition, in 2002 new population data from the 2000 decennial Census became available for use in NSDUH sample weighting procedures. Therefore the data from 2002 and later should not be compared with data collected in 2001 or earlier to
assess changes over time.
For selected variables, statistical imputation was performed following logical inference to replace missing responses. These variables are identified in the codebook as
"...LOGICALLY ASSIGNED" 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, a corresponding imputation indicator variable indicates whether a case's value on the variable resulted from an interview response or was imputed. Missing values for some demographic variables were imputed by the unweighted hot-deck
technique used in previous surveys. Beginning in 1999, imputation of missing values for most variables was accomplished using predictive mean neighborhoods (PMN), a new procedure developed specifically for this survey. Both the hot-deck and PMN imputation procedures are described in the codebook.
To protect the privacy of respondents, all variables that could be used to identify individuals have been encrypted or collapsed in the public use file. To further ensure respondent confidentiality, the data producer used data substitution and deletion of state identifiers and a subsample of records in the creation of the public use file.
Previously published estimates may not be exactly reproducible from the variables in the public use file due to the disclosure protection procedures that were implemented.
The setup and dictionary files for Stata are designed to be compatible with StataSE, Version 8. This is a large data file requiring that approximately 250 megabytes of Random Access Memory be allocated to Stata. Operations within Stata,
including conversion of the ASCII data to Stata format, are likely to be slow. Analysts may wish to download subsets of data from the SAMHDA Survey Documentation and Analysis (SDA) system for use with Stata.
In the income section, which was interviewer-administered, a split-sample study had been embedded within the 2006 and 2007 surveys to compare a shorter version of the income questions with a longer set of questions that had been used in previous surveys. This shorter version was adopted for the 2008 NSDUH and will be used for future NSDUHs.
A multistage area probability sample for each of the 50
states and the District of Columbia has been used since 1999. The 2005 NSDUH was the first survey in a coordinated five-year sample design. Although there is no overlap with the 1999-2004 samples, the coordinated design for 2005 through 2009 facilitated a 50 percent overlap in second-stage units (area segments [see below]) between each two successive years from 2005 through 2009. This design was intended to increase precision of estimates in year-to-year trend analyses because of the expected positive correlation resulting from the overlapping sample between successive survey years. The 2008 design allows for computation of estimates by state in all 50 states plus the District of Columbia. States may therefore be viewed as the first level of stratification as well as a reporting variable. Eight states, referred to as the large sample states, had a sample designed to yield 3,600 respondents per state for the 2008 survey. This sample size was considered adequate to support direct state estimates. The remaining 43 states (which include the District of Columbia) had a sample designed to yield 900 respondents per state in the 2008 survey. In these 43 states, adequate data were available to support reliable state estimates based on SAE methodology. Within each state, sampling strata called state sampling (SS) regions were formed. Based on a composite size measure, states were partitioned geographically into roughly equal-sized regions. In other words, regions were formed such that each area yielded, in expectation, roughly the same number of interviews during each data collection period. The eight large sample states were divided into 48 SS regions each. The remaining states were divided into 12 SS regions each. Therefore, the partitioning of the United States resulted in the formation of a total of 900 SS regions. Unlike the 1999 through 2004 surveys, the first stage of selection for the 2005 through 2009 NSDUHs was Census tracts. The first stage of selection began with the construction of an area sample frame that contained one record for each Census tract in the United States. If necessary, Census tracts were aggregated within SS regions until each tract had, at a minimum, 150 dwelling units in urban areas and 100 dwelling units in rural areas. These Census tracts served as the primary sampling units (PSUs) for the coordinated five-year sample. One area segment (one or more Census blocks) was selected within each sampled Census tract. In advance of the survey period, specially trained listers had visited each area segment and listed all addresses for housing units and eligible group quarters units in a prescribed order. Systematic sampling was used to select the allocated sample of addresses from each segment. Beginning in 2002, each respondent who completed a full interview was given a $30 cash payment as a token of appreciation for his or her time. To improve the precision of the estimates, the sample allocation process targeted five age groups: 12 to 17 years, 18 to 25 years, 26 to 34 years, 35 to 49 years, and 50 years or older. The size measures used in selecting the area segments were coordinated with the dwelling unit and person selection process so that a nearly self-weighting sample could be achieved in each of the five age groups. The achieved sample size for the 2008 survey was 67,928 persons. The public use file contains 55,739 records due to a subsampling step used in the disclosure protection procedures. A key step in the data processing procedures established the minimum item response requirements in order for cases to be retained for weighting and further analysis (i.e., "usable" cases). These requirements, as well as full sampling methodology, are detailed in the codebook.
Due to unequal selection probabilities at multiple stages of sample selection and various adjustments, such as those for nonresponse and poststratification, the 2008 NSDUH sample design is not self-weighting. Analysts are advised to use the final sample weight when attempting to use the 2008 NSDUH data to draw inferences about the target population or any subdomains of the target population. All estimates published in SAMHSA reports (such as the results from the 2008 NSDUH) are weighted using the final analysis weight for the full sample (ANALWT). For the public use file, the corresponding final sample weight is denoted as ANALWT_C, with the "C" denoting confidentiality protection. This sample weight represents the total number of target population persons each record on the file represents. Note that the sum of ANALWT_C, over all records on the data file, represents an estimate of the total number of people in the target population.
In the mental health module of the 2008 NSDUH, the adult sample was split into sample A (MHSAMP08 = 1) who received the World Health Organization-Disability Assessment Scale (WHODAS) questions LIREMEM through LIAD68, and sample B (MHSAMP08 = 2) who received the Sheehan Disability Scale (SDS) questions MHAD66a through MHAD68. The mental health adult split-sample weight (MHSAWT_C) was created to accommodate analysis using either one of the split samples, and it is the product of person-level analysis weight (ANALWT_C) and a poststratification adjustment that was done separately for both sample A and sample B. The mental health adult split-sample weight for both sample A and sample B was controlled to the Census population estimates for the civilian, noninstitutionalized population aged 18 or older. It is noted that the MHSAWT_C was set to zero for all 12 to 17 year olds and the 10 adults who were not assigned to either of the split samples. The MHSAWT_C can be used for generating mental health estimates when using just sample A data or when using just sample B data separately. However, if mental health estimates are generated using both sample A and sample B combined data, then the person-level analysis weight (ANALWT_C) should be used.
Mode of Data Collection:
audio computer-assisted self interview (ACASI),
computer-assisted personal interview (CAPI),
computer-assisted self interview (CASI)
Strategies for ensuring high rates of participation resulted in a weighted screening response rate of 88.62 percent and a weighted interview response rate for the CAI of 74.24 percent. (Note that these response rates reflect the original sample, not the subsampled data file referenced in this document.)
Extent of Processing: ICPSR data undergo a confidentiality review and are altered when necessary to limit the risk of
disclosure. ICPSR also routinely creates ready-to-go data files along with setups in the major
statistical software formats as well as standard codebooks to accompany the data. In addition to
these procedures, ICPSR performed the following processing steps for this data collection:
Performed consistency checks.
Standardized missing values.
Created online analysis version with question text.
Checked for undocumented or out-of-range codes.
Restrictions: Users are reminded that these data are to be used solely for statistical analysis and reporting of aggregated information and not for the investigation of specific individuals or treatment facilities.