BOOK MEASUREMENT IN MEDICINE
HVC de Vet
CB Terwee
LB Mokkink
DL Knol

CHAPTER 4  ASSIGNMENT 3: FACTOR ANALYSIS GO-QOL QUESTIONNAIRE

PUBLISHED AS: Terwee CB, Gerding MN, Dekker FW, Prummel MF, Wiersinga WM. 
Development of a disease-specific quality of life questionnaire for patients with Graves' ophthalmopathy. Br J Ophthalmol 1998;82:773-779

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*ASSIGNMENT 3: FACTOR ANALYSES GO-QOL.

*3a Step 1: Correlation matrix.

CORRELATIONS
  /VARIABLES=bicycling driving moving_house walking reading tv hobby
  interference changed_app stared unpeas_react selfconfidence friends
  isolation photos mask_changes
  /PRINT=TWOTAIL SIG
  /MISSING=PAIRWISE .


*3b PCA.
*Step 2: The number of factors to be extracted.

FACTOR
  /VARIABLES bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
/MISSING LISTWISE /ANALYSIS bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
  /PRINT INITIAL EXTRACTION 
  /PLOT EIGEN 
  /CRITERIA MINEIGEN(1) ITERATE(25)
  /EXTRACTION PC
  /METHOD=CORRELATION .


*Step 3 Rotation.

FACTOR
  /VARIABLES bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
/MISSING LISTWISE /ANALYSIS bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
  /PRINT INITIAL EXTRACTION ROTATION
  /PLOT EIGEN ROTATION
  /CRITERIA MINEIGEN(1) ITERATE(25)
  /EXTRACTION PC
  /CRITERIA ITERATE(25)
  /ROTATION VARIMAX
  /METHOD=CORRELATION .


*3d. PCA analysis forcing a 2 factor model. 

FACTOR
  /VARIABLES bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
/MISSING LISTWISE /ANALYSIS bicycling driving moving_house walking reading tv hobby interference
  changed_app stared unpeas_react selfconfidence friends isolation photos
  mask_changes 
  /PRINT INITIAL CORRELATION EXTRACTION ROTATION
  /PLOT EIGEN ROTATION
  /CRITERIA FACTORS(2) ITERATE(25)
  /EXTRACTION PC
  /CRITERIA ITERATE(25)
  /ROTATION VARIMAX
  /METHOD=CORRELATION .