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DATA MANAGEMENT. Using EpiData and SPSS. References. Public domain (pdf) book on data management: Bennett, et al. (2001). Data Management for Surveys and Trials. A Practical Primer Using EpiData . The EpiData Documentation Project. : http://www.epidata.dk/downloads/dmepidata.pdf

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Data management l.jpg

DATA MANAGEMENT

Using EpiData and SPSS


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References

Public domain (pdf) book on data management:

Bennett, et al. (2001). Data Management for Surveys and Trials. A Practical Primer Using EpiData. The EpiData Documentation Project. : http://www.epidata.dk/downloads/dmepidata.pdf

EpiData Association Website: http://www.epidata.dk/

Importing raw data into SPSS: http://www.ats.ucla.edu/stat/spss/modules/input.htm


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Data Management

  • Planning data needs

  • Data collection

  • Data entry and control

  • Validation and checking

  • Data cleaning and variable transformation

  • Data backup and storage

  • System documentation

  • Other


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Types of Data Base Management Systems (DBMSs)

  • Spreadsheets (e.g., Excel, SPSS Data Editor)

    • Prone to error, data corruption, & mismanagement

    • Lack data controls, limited programmability

    • Suitable only for small and didactic projects

    • Also good for last step data cleaning

  • Commercial DBMS programs (e.g., Oracle, Access)

    • Limited data control, good programmability

    • Slow & expensive

    • Powerful and widely available

  • Public domain programs (e.g., EpiData, Epi Info)

    • Controlled data entry, good programmability

    • Suitable for research and field use


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We will use two platforms:

  • EpiData

    • controlled data entry

    • data documentation

    • export (“write”) data

  • SPSS

    • import (“read”) data

    • analysis

    • reporting


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What is EpiData ?

  • EpiData is computer program (small in size 1.2Mb) for simple or programmed data entry and data documentation

  • It is highly reliable

  • It runs on Windows computers

    • Runs on Macs and Linus with emulator software (only)

  • Interface

    • pull down menus

    • work bar


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History of EpiInfo & EpiData

  • 1976–1995: EpiInfo (DOS program) created by CDC (in wake of swine flu epidemic)

    • Small, fast, reliable, 100,000+ users worldwide

  • 1995–2000: DOS dies slow painful death

  • 2000: CDC releases EpiInfo2000

    • Based on Microsoft Jet (Access) data engine

    • Large, slow, unreliable (resembled EpiInfo in name only)

  • 2001: Loyal EpiInfo user group decides it needs real “EpiInfo for Windows”

    • Creates open source public domain program

    • Calls program “EpiData”


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Goal: Create & Maintain Error-Free Datasets

  • Two types of data errors

    • Measurement error (i.e., information bias) – discussed last couple of weeks

    • Processing errors = errors that occur during data handling – discussed this week

  • Examples of data processing errors

    • Transpositions (91 instead of 19)

    • Copying errors (O instead of 0)

    • Additional processing errors described on p. 18.2


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Avoiding Data Processing Errors

  • Manual checks (e.g., handwriting legibility)

  • Range and consistency checks* (e.g., do not allow hysterectomy dates for men)

  • Double entry and validation*

    • Operator 1 enters data

    • Operator 2 enters data in separate file

    • Check files for inconsistencies

  • Screening during analysis (e.g., look for outliers)

* covered in lab


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Controlled Data Entry

  • Criteria for accepting & rejecting data

  • Types of data controls

    • Range checks (e.g., restrict AGE to reasonable range)

    • Value labels (e.g., SEX:1 = male, 2 = female)

    • Jumps (e.g., if “male,” jump to Q8)

    • Consistency checks (e.g., if “sex = male,” do not allow “hysterectomy = yes”)

    • Must enters

    • etc.


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Data Processing Steps

  • File naming conventions

  • Variables types and names

  • QES (questionnaire) development

  • Convert .QES file to .REC (record) file

  • Add .CHK file

  • Enter data in REC file

  • Validate data (double entry procedure)

  • Documentation data (code book)

  • Export data to SPSS

  • Import data into SPSS


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Filenaming and File Management

  • c:\path\filename.ext

  • A web address is a good example of a filename, e.g., http://www2.sjsu.edu/faculty/gerstman/StatPrimer/data.ppt

  • Some systems are case sensitive (Unix)

    • Others are not (Windows)

  • Always be aware of

    • Physical location(local, removable, network)

    • Path (folders and subfolders)

    • Filename (proper)

    • Extension

  • Demo Windows Network Explorer: right-click Start Bar > Explore




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EpiData Variable Names

  • Variable name based on text that occurs before variable type indicator code

  • EpiData variable naming default vary depending on installation

  • Create variable names exactly as specified

    To be safe, denote variable names in {curly brackets}

  • For example, to create a two byte numeric variable called age, use the question:

What is your {age}? ##


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Demo / Work Along

  • Create QES file [demo.qes]

  • Convert QES to REC [demo.rec]

  • Create CHK file [demo.chk]

  • Create double entry file [demo2.rec]

  • Enter data

  • Validate data


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We will stop here and pick up the second part of the lecture next week

“Stay tuned”


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Codebooks

  • Contain info that helps users decipher data file content and structure

  • Includes:

    • Filename(s)

    • File location(s)

    • Variable names

    • Coding schemes

    • Units

    • Anything else you think might be useful



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File Structure Codebook

Full codebook contains descriptive statistics (demo)


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Full Codebook

Notice descriptive statistics


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Conversion of Data File

  • Requires common intermediate file format

  • Examples of common intermediate files

    • .TXT = plain text

    • .DBF = dBase program

    • .XLS = Excel

  • Steps

    • Export .REC file  .TXT file

    • Import .TXT file into SPSS

    • Save permanent SAV file



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Plain (“raw”) TXT data

  • plain ASCII data format

  • no column demarcations

  • no variable names

  • no labels


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TXT file with codebook

tox-samp.txt

tox-samp.not


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SPSS Data Export / Import

TXT

(raw data)

SAV

REC

SPS

(syntax)


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Top of tox-samp.sps

Lines beginning with * are

comments (ignored by

command interpreter)

Next set of commands show

file location and structure

via SPSS command syntax


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Bottom part of tox-samp.sps file

Labels being imported

into SPSS

Delete * if you want this

command to run




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Ethics of Data Keeping

  • Confidentiality (sanitized files – free of identifiers)

  • Beneficence

  • Equipoise

  • Informed consent (To what extent?)

  • Oversight (IRB)


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