concluded that the discrepancies between results for the SF-36 scale scores and component scores are a result of the negatively weighted scales used in the PCS and MCS scoring algorithm. These patients had large improvements on the emotional well-being scale (1.67 SD). For example, a study of 482 patients initiating antidepressant treatment found improvements from baseline to 3 months of 0.28–0.49 SD units on the physical health scales (physical functioning, role limitations due to physical health problems, pain, general health), but the PCSuc was essentially unchanged (from 51 to 50). Recent studies have shown inconsistent results between the 8 SF-36 scale scores and the PCS and MCS. The model assumes that physical and mental health constructs are uncorrelated (Φ = 0). Figure 1 depicts the conceptual framework on which the orthogonal component summary scores are based. The standard scoring algorithm for the SF-36 and SF-12 version 1 summary measures is based on a factor analytic technique that forces the scores to be orthogonal. The SF-12 is a 12-item subset of the SF-36 that has two summary measures: the Physical (PCS-12) and Mental (MCS-12) Component Summary scores. The 36 th item, which asks about health change, is not included in the scale or summary scores. These eight scales can be aggregated into two summary measures: the Physical (PCS) and Mental (MCS) Component Summary scores. The SF-36 is composed of 8 multi-item scales (35 items) assessing physical function (10 items), role limitations due to physical health problems (4 items), bodily pain (2 items), general health (5 items), vitality (4 items), social functioning (2 items), role limitations due to emotional problems (3 items) and emotional well-being (5 items). The SF-36 and the SF-12 are the most frequently used multi-item HRQOL instruments. Health-related quality of life (HRQOL) refers to functioning and well-being in physical, mental and social dimensions of life. (Subscripts C = correlated and UC = uncorrelated) 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. ConclusionĬorrelated 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. Similar results were found for PCS c-12, and MCS c-12 summary scores. 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. The estimated correlation between SF-36 PCS c and MCS c scores was 0.62. PCS c-12 and MCS c-12 scores were estimated using an approach similar to the one used to derive the original SF-12 summary scores. Correlated physical health (PCS c) and mental health (MCS c) scores were constructed by multiplying each SF-36 scale z-score by its respective scoring coefficient from the obliquely rotated two factor solution. 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. We estimate SF-36 and SF-12 summary scores using a correlated (oblique) physical and mental health factor model. The SF-36 and SF-12 summary scores were derived using an uncorrelated (orthogonal) factor solution.
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