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Creating Something from Nothing: Working with Synthetic Files

Creating Something from Nothing: Working with Synthetic Files. Bo Wandschneider University of Guelph. DLI Training: April 2004, Kingston. Outline. NLSCY background Types of microdata files Which microdata file to use Providing services for synthetic files.

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Creating Something from Nothing: Working with Synthetic Files

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  1. Creating Something from Nothing:Working with Synthetic Files Bo Wandschneider University of Guelph DLI Training: April 2004, Kingston

  2. Outline • NLSCY background • Types of microdata files • Which microdata file to use • Providing services for synthetic files This presentation is a modification of a workshop that Chuck Humphrey and I presented at the May 2003 National DLI Training and a Presentation Chuck presented at Accoleds – DLI training, 2003.

  3. NLSCY • The National Longitudinal Survey of Children and Youth (NLSCY) is a long-term study of Canadian children that follows their development and well-being from birth to early adulthood. The NLSCY began in 1994 and is jointly conducted by Statistics Canada and Human Resources Development Canada.

  4. NLSCY • There are 4 cycles • There are 8 different files • 2 of these are available as a PUMF • Primary • Self-Reporting • The rest include: secondary and those based on people reporting about child (teacher, principal…)

  5. Types of Microdata Files • Confidential Microdata Products • Master Files • Share Files • Public Access Microdata Products • Public use anonymized microdata (PUMFS) • Synthetic Files

  6. Microdata raw data organized in a file where the records or lines in the file are observations of a specific unit of analysis and the information on the lines are the values of variables requires some form of processing or analysis to be used Microdata Products

  7. NLSCY –cycle 3 - primary Microdata Products

  8. Master Files These files contain the fullness of detail captured about the unit of observation. The information in these files could identify the individual who provided the original information and, therefore, are considered confidential. Confidential Microdata

  9. Confidential Microdata Master File – Example

  10. Confidential Microdata Master File – detailed identifiers

  11. Confidential Microdata Master File – geography

  12. Confidential Microdata Master File - fullness of data

  13. Confidential Microdata Master File - fullness of data

  14. Confidential Microdata Master File - fullness of data

  15. Share Files these are confidential files in which the respondents have signed a consent form permitting Statistics Canada to allow access to their information for approved research. Used with NPHS and NLSCY Confidential Microdata

  16. Anonymized Microdata these microdata are specially prepared to minimize the possibility of disclosing or identifying any of the cases or observations the original data from the master file are edited to create a public use microdata file Public Access Microdata

  17. Steps in Anonymizing Microdata removal of all personal identifiers include only gross levels of geography collapse detailed information into fewer general categories or cap values suppress the values of a variable Public Access Microdata

  18. Statistics Canada PUMFs only available for select social surveys that undergo a review of the Data Release Committee, an internal Statistics Canada committee; no ‘enterprise’ public use microdata; Public Access Microdata

  19. Statistics Canada PUMFs almost all are cross-sectional, that is, represent data collected at one point in time; longitudinal data are difficult to anonymize while maintaining any useful information. Public Access Microdata

  20. PUMFs – personal identifiers Public Access Microdata

  21. PUMFs – gross geography Public Access Microdata

  22. PUMFs – collapsed data Public Access Microdata

  23. PUMFs – suppressed variables Note – from the MASTER file – NOT the PUMF Public Access Microdata

  24. Public Access Microdata Synthetic Files • These microdata do not contain actual ‘real’ cases but are pseudo-cases that for some surveys, provide aggregate results close to the ‘real’ cases

  25. Public Access Microdata Synthetic Files • They have been prepared to create analysis runs with the master file without possibly disclosing or identifying any of the cases

  26. Public Access Microdata Synthetic Files • The results are not to be reported, but are strictly to be used to prepare analyses of master files; • Usually associated with longitudinal files.

  27. Public Access Microdata Steps in creating Synthetic Files • Observations are transformed • No records actually exist • Keep fullness of variable description • How the files are made is kept confidential

  28. Public Access Microdata Synthetic Files – NLSCY

  29. Public Access Microdata Synthetic Files – NPHS 1999 General File

  30. Implications for Analysis What are the implications in doing analysis with these different types of microdata files?

  31. Implications for Analysis Master File • All observations • Has the most variables with the most detail • Lots of geography and personal characteristics • Little grouping or capping of categories

  32. Implications for Analysis Master File • Restricted access: only available to authorized Statistics Canada employees, which includes ‘deemed employees’; • Use of the analysis is controlled through a contract;

  33. Implications for Analysis Master File • Includes linkage variables across files within a study, e.g., NLSCY linkage among the files for different units of analysis (kids, parents, teachers…).

  34. Implications for Analysis Public Use Microdata (PUMF) • Valuable content for a tremendous amount of research; • Suppresed observations • Suppressed variables • Suppresed Content • Gross Geography • Collapsed categories • Capped variables • Where issues arise is when smaller area geography is desired; rare subpopulations are being studied; or the variables that are needed have been used to anonymize respondents;

  35. Implications for Analysis Public Use Microdata (PUMF) • Licensed product: agree to certain terms of use; • No linkage to multiple units of analysis, except for a few exceptions (e.g., GSS Time Use and Family);

  36. Implications for Analysis Synthetic Files “Looks like a duck and quacks like a duck”, but it isn’t a duck or any other type of fowl.

  37. Implications for Analysis Synthetic Files • Looks like master files • Lots of observations (maybe) • Lots of variables • Little grouping or capping of categories • Lots of geographic detail

  38. Synthetic Files Precautions • Results not authentic – but may be close in the aggregate for some synthetic files; • Use for testing analysis setups only; • Still need the master files for publishable results.

  39. Where do we get Access? Master File • Restricted access governed under the Statistics Act; • Remote Job Submission (a.k.a, RDA) • Research Data Centres • Apply to SSHRC to obtain a peer-reviewed proposal and STC for security clearance.

  40. Where do we get Access? Public Use Microdata Files (PUMF) • Get from DLI • Analyze where it is convenient • Can use a variety of analysis software, including SAS, SPSS, Stata, HLM, LISREL, etc.

  41. Where do we get Access? Synthetic Files • Author Divisions ‘may’ create it • Most relevant when dealing with new Panel Data, but not necessarily, e.g., the Census has potential • NLSCY, NPHS & CCHS synthetic files on DLI FTP site

  42. Where do we get Access? Synthetic files • Work locally with the file • Build SAS and SPSS setups

  43. Which File is Appropriate? • 1st stop is still the PUMF; • This file has the easiest access for us; • Probably meets the needs of most patrons; • Not as administratively burdensome as synthetic or master file; • Perfect for clients just looking for ‘data’ – courses in quantitative analysis;

  44. Which File is Appropriate? • If more detail is needed, refer to the Master File Documentation; • Inform patrons that the cost of use is higher, both in terms of accessibility and analytical requirements; • Interest most likely to come from grad students and ‘experienced’ researchers

  45. Which File is Appropriate? • Download the Synthetic files from DLI • Make them aware of problems with synthetic files – RESULTS ARE NOT PUBLISHABLE • Encourage them to submit an application for RDC access – there is a time lag

  46. Which File is Appropriate? RDC

  47. Which File is Appropriate? • Some of you may work with patron using synthetic files before passing her/him off to RDC.

  48. Services for Synthetic Files DLI Contacts can provide four basic services with synthetic files. • Build SPSS and SAS system files from the raw synthetic data files that are distributed through DLI; • Provide information about the use of Remote Job Submission and RDC’s;

  49. Services for Synthetic Files • Assist with finding variables in the synthetic files; • Provide instruction about ways of capturing SPSS or SAS code from “dummy” analysis runs with the synthetic files. It is this code that is submitted to STC through remote job submission.

  50. Services for Synthetic Files 1. Building SPSS and SAS system files for synthetic data • The NLSCY synthetic data are distributed as a raw ASCII file with accompanying command files for SPSS and SAS • Separate synthetic data files exist for each component of the NLSCY – not all components have PUMF’s

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