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2008 Summer North American Stata Users Group meetingChicago, 24-25 July 2008
Using SPSS files in Stata
Sergiy RadyakinThe World Bank
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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)
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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
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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
http://www.data-archive.ac.uk/support/conversionguide.pdf
• 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.)
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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)
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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
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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
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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)]
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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.
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Memory Tradeoff
• Similarly to Stata, usespss attempts to load the whole data file into memory; this speeds up the 2-pass processing (1st pass – optimization of the storage types, 2nd 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.
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Stata data
Stata code
Memory Use
time
Limit, e.g. 2GB
usespss.adostarts
Stata memory is temporarily set to a
low value
Plugin data
Mem
ory
usespss.ado ends
Stata memory is set to a higher value
Consider the following code:
set mem 800musespss using “mydata.sav”, lowmemory(10) memory(800)
Free memory
Free memory
Plugin code
10m
800m
Any dataset in Stata’s
memory is cleared
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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()
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DESSPSS Example Report
. desspss using artificial.sav
DESSPSS Report==============SPSS System file: artificial.savCreated (date): 17-Jul- 8Created (time): 22: 4: 0SPSS product: SPSS-X SYSTEM FILE. SPSS 5.0 MS/Windows made by DBMS/COPY File label (if present): File size (as stored on disk): 382692 bytesData size: 381432 bytesData stored in compressed formatThis file is likely to originate from a Windows platform (LoHi byte order)
Number of cases (observations): 10000Number of variables: 10Case size: 88 bytes----------------------------------------------------------------------
Variables:
GENDER MARRIED B_YEAR W_HOURS CITY_CODAGE EMP_STAT WAGE FULLTIME CITY_NAM
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• 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 5.00[HKEY_CLASSES_ROOT\.sav]@="sav_auto_file"[HKEY_CLASSES_ROOT\sav_auto_file]@="SPSS Dataset"[HKEY_CLASSES_ROOT\sav_auto_file\shell][HKEY_CLASSES_ROOT\sav_auto_file\shell\open][HKEY_CLASSES_ROOT\sav_auto_file\shell\open\command]@="\"C:\\Stata10se\\wsestata.exe\" usespss \"%1\"“---------------------- end of sav_file.reg -------------------------
Demonstration:
artificial.sav