1989-09-26 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:
- Standardized missing values.
- Performed recodes and/or calculated derived variables.
- Checked for undocumented or out-of-range codes.
2005-11-04 On 2005-03-14 new files were added to one
or more datasets. These files included additional setup files as well
as one or more of the following: SAS program, SAS transport, SPSS portable,
and Stata system files. The metadata record was revised 2005-11-04 to
reflect these additions.
1997-05-30 SAS data definition statements are now available
for this collection, and the SPSS data definition statements were
2008-10-30 All parts have been moved to restricted access and are available only using the restricted access procedures.
2008-11-12 Minor changes have been made to the metadata.