Presentation on theme: "2008 Summer North American Stata Users Group meeting Chicago, 24-25 July 2008 Using SPSS files in Stata Sergiy Radyakin The World Bank."— Presentation transcript:
2008 Summer North American Stata Users Group meeting Chicago, July 2008 Using SPSS files in Stata Sergiy Radyakin The World Bank
2 How to get the data in? Use Stata to manipulate the data and read it in Use the data producing application to export the data in the proper format that Stata can later import Use specialized conversion software to convert to a proper format Use another statistical package that supports both formats to make it convert the dataset Write own conversion program in/as: –Stata (slow, portable) –Mata (faster, portable) –Plugin (very fast, not portable, dependent on Stata’s bit-width) –Standalone (very fast, not portable, independent of Stata’s bitwidth)
3 Which data formats does Stata support (as of v10)? Stata native formats (use) ASCII data with dictionaries (insheet/infix) SAS XPORT format (fdause) Data import via ODBC, provided that a required driver is installed and configured But, no SPSS support
4 When SPSS is available: SPSS v14 and later supports exporting data to Stata format SPSS_to_Stata_00.sbs script by Alasdair Crockett is available for earlier releases, requires both SPSS and Stata for conversion Data Services Guides: SPSS_to_Stata Conversion Utility Guide This can be automated with an.ado wrapper similar to USESAS by Dan Blanchette, which requires SAS to be installed to import data to Stata These are not “true readers”, since they require SPSS or SAS to be installed (with license costs, etc.)
5 Specialized Conversion Software Stat/Transfer –http://www.stattransfer.com/ –$295 (New unit, Windows) DBMS/Copy –http://www.dataflux.com/Product- Services/Products/dbms.asp –$495 (New individual, Windows) Both support command line parameters to convert in a batch-mode and thus can be “wrapped” for use with Stata, see e.g. STCMD by Roger Newson (as of July 13, 2008)
6 USESPSS USESPSS is a new command for Stata to read in SPSS data (*.sav files) It is a “true reader” – does not require any other software (other than OS Windows) Free Implemented as a plugin, with portions of code (e.g. file decompression) written in assembler for performance optimization Note: SPSS format documentation is not released, and only fragmented information is available in the Internet
7 USESPSS Features Reads *.sav files originating from both Windows and UNIX versions of SPSS (LoHi and HiLo byte orders) Supports compressed and non-compressed SPSS files Preserves variable and value labels Optimizes data storage types (2-pass) Supports long variable names Automatically renames not allowed variable names and resolves naming collisions Preserves number of decimals in numeric formats. Transfers, but does not format date/time variables
8 USESPSS Syntax usespss can be used as any other command in the command line, user’s.do files and.ado programs: usespss [using] “filename.sav” [,clear saving(“filename.dta”) iff(condition) inn(condition) memory(memsize) lowmemory(memsize)]
9 Memory Tradeoff Stata and plugins share the same address space As a consequence, plugins can read Stata’s data directly (if they know where it is located) and call Stata’s subroutines (if exposed). However, the more memory is allocated for Stata data, the less memory is available to the plugins, because the size of the address space is limited (typically 2GB on a 32-bit Windows system). In other words, plugins compete for memory between themselves and with Stata.
10 Memory Tradeoff Similarly to Stata, usespss attempts to load the whole data file into memory; this speeds up the 2-pass processing (1 st pass – optimization of the storage types, 2 nd pass – actual conversion) But, when user loads the SPSS data Stata data (if any) is discarded. So Stata’s memory use can be temporarily decreased within usespss.ado It is important to do this when working with large files, otherwise the plugin will not be able to allocate enough memory to load the SPSS data file.
11 Stata data Stata code Memory Use time Limit, e.g. 2GB usespss.ado starts Stata memory is temporarily set to a low value Plugin data Memory usespss.ado ends Stata memory is set to a higher value Consider the following code: set mem 800m usespss using “mydata.sav”, lowmemory(10) memory(800) Free memory Free memory Plugin code 10m 800m Any dataset in Stata’s memory is cleared
12 DESSPSS desspss is a new Stata command to describe the contents of an SPSS system *.sav file does not destroy data in the memory works much faster than usespss using filename.sav, saving(filename.dta) describe because no optimization/conversion is actually performed, but does not list the variable types (these are determined after optimization) saves all descriptive information in r()
13 DESSPSS Example Report. desspss using artificial.sav DESSPSS Report ============== SPSS System file: artificial.sav Created (date): 17-Jul- 8 Created (time): 22: 4: 0 SPSS product: SPSS-X SYSTEM FILE. SPSS 5.0 MS/Windows made by DBMS/COPY File label (if present): File size (as stored on disk): bytes Data size: bytes Data stored in compressed format This file is likely to originate from a Windows platform (LoHi byte order) Number of cases (observations): Number of variables: 10 Case size: 88 bytes Variables: GENDER MARRIED B_YEAR W_HOURS CITY_COD AGE EMP_STAT WAGE FULLTIME CITY_NAM
14 Embedded artificially created dataset in SPSS format: Click on the icon opens the SPSS file in Stata if: 1.usespss is installed in Stata, and 2.file assosiation was set: Substitute with the full name of the Stata’s executable Questions? beginning of sav_file.reg Windows Registry Editor Version Dataset" [HKEY_CLASSES_ROOT\sav_auto_file\shell] [HKEY_CLASSES_ROOT\sav_auto_file\shell\open] usespss \"%1\"“ end of sav_file.reg Demonstration: