Identification of Scoliosis Research Society-22r Health-Related Quality of Life questionnaire domains using factor analysis methodology.
METHODS
Cross-sectional mail questionnaire.


OBJECTIVE
Examination of the underlying construct validity of the Scoliosis Research Society-22r (SRS-22r) Health-Related Quality of Life (HRQoL) Questionnaire using factor analysis.


BACKGROUND
The original SRS-24 HRQoL questionnaire has undergone a series of modifications in an effort to further improve its psychometric properties and validate its use in patients from 10 years of age until well into adulthood. The SRS-22r questionnaire is the result of this effort. To date, the underlying construct validity of the original English version has not been analyzed by factor analysis.


METHODS
A questionnaire including all questions on the SRS-24, -23, -22, and -22r questionnaires (49 total questions) was mailed to a consecutive series of 235 patients who had received primary posterior or anterior instrumentation and arthrodesis. Domain structure of the SRS-22r questions was analyzed using iterated principal factor analysis with orthogonal rotation.


RESULTS
One hundred twenty-one (51%) of the patients, age 23.34 +/- 4.52 years (range, 14.16-34.57 years), returned the questionnaire at 8.63 +/- 4.00 years (range, 2.32-15.94 years) following surgery. Factor analysis using all 22 questions resulted in 3 factors with many shared items because of significant collinearity of the satisfaction/dissatisfaction with management questions with the others. After 18 iterations, factor analysis using the 20 nonmanagement questions revealed 4 factors that explained 98% of the variance. These factors parallel the assigned domains of the SRS-22r questionnaire. Three questions (2 self-image and 1 function) were identified that had high loading in 2 factors. However, internal consistency was best when 2 of the questions (1 self-image and 1 function) were retained in their assigned SRS-22r domains and the third decreased self-image internal consistency by only 0.01%. The internal consistencies (Cronbach alpha) of the assigned SRS-22r nonmanagement domains were excellent or very good: function 0.83, pain 0.87, self-image 0.80, and mental health 0.90. For the management domain it was good: 0.73.


CONCLUSIONS
Factor analysis of the SRS-22r HRQoL confirms placement of the 20 nonmanagement domain questions in the assigned 4 domains, all with excellent or very good internal consistency.
Lai
Sue-Min
SM
Department of Preventive Medicine and Public Health, Kansas University Medical Center, Kansas City, KS 66160, USA. slai@kumc.edu
Asher
Marc A
MA
Burton
Douglas C
DC
Carlson
Brandon B
BB
D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008297:Male; D025341:Principal Component Analysis / Q000592:standards; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D012600:Scoliosis / Q000175:diagnosis / Q000523:psychology*; D012955:Societies, Medical / Q000592:standards*; D011795:Surveys and Questionnaires / Q000592:standards*; D014481:United States; D055815:Young Adult