Correlated physical and mental health summary scores for the SF-36 and SF-12 Health Survey, V.I.
BACKGROUND
The SF-36 and SF-12 summary scores were derived using an uncorrelated (orthogonal) factor solution. We estimate SF-36 and SF-12 summary scores using a correlated (oblique) physical and mental health factor model.


METHODS
We administered the SF-36 to 7,093 patients who received medical care from an independent association of 48 physician groups in the western United States. Correlated physical health (PCSc) and mental health (MCSc) scores were constructed by multiplying each SF-36 scale z-score by its respective scoring coefficient from the obliquely rotated two factor solution. PCSc-12 and MCSc-12 scores were estimated using an approach similar to the one used to derive the original SF-12 summary scores.


RESULTS
The estimated correlation between SF-36 PCSc and MCSc scores was 0.62. There were far fewer negative factor scoring coefficients for the oblique factor solution compared to the factor scoring coefficients produced by the standard orthogonal factor solution. Similar results were found for PCSc-12, and MCSc-12 summary scores.


CONCLUSIONS
Correlated physical and mental health summary scores for the SF-36 and SF-12 derived from an obliquely rotated factor solution should be used along with the uncorrelated summary scores. The new scoring algorithm can reduce inconsistent results between the SF-36 scale scores and physical and mental health summary scores reported in some prior studies.(Subscripts C = correlated and UC = uncorrelated).
Farivar
Sepideh S
SS
Global Health Economics, Amgen, Inc., Thousand Oaks, CA, USA. sfarivar@amgen.com
Cunningham
William E
WE
Hays
Ron D
RD
D000293:Adolescent; D000328:Adult; D000465:Algorithms; D005260:Female; D006297:Health Services Accessibility; D006305:Health Status Indicators; D006801:Humans; D007193:Independent Practice Associations / Q000706:statistics & numerical data*; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D011788:Quality of Life / Q000523:psychology*; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D014481:United States; D014600:Utilization Review