Underinsurance among Women who have availed of PhilHealth’s MCP developed by Ware et al. in 1994 with the following goals: to account for at least 90% of the variance in the SF-36 physical and mental summary scores, to provide summary scores that would coincide with the average scores on the SF-36, and to be brief enough to be printed on a single page and administered in less than two minutes (McDowell, 2012; Ware et al., 1994) The principal scores of the SF-12 are the physical health composite score (PCS-12) and the mental health composite score (MCS-12). In a revised version developed in 1998, an eight-domain profile can be produced, providing scores for Physical Functioning, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health (Ware, Kosinki, and Gandek, 2002). The scoring for the SF-12 was changed between its first and second versions. The latter may be scored in a conventional manner involving three steps. First, out-of-range values are treated as missing. Second, scores for some items are reversed while some are recalibrated, and the total scores for each domain are calculated. Lastly, these total scores are transformed into a 0 to 100 scale. Alternatively, norm-based scoring makes use of regression weights to standardize each of the eight scale scores to a mean of 50 and standard deviation of 10 using weights based on the general population of a particular country. (Maddigan, Feeny, and Johnson, 2004). PCS and MCS scores are also based on factor score weights for combining the eight scale scores (Ware et al., 2002). This norm-based method of scoring has been shown to provide a significantly stronger correlation with SF-36 scores than a simpler equal-interval scoring approach (Ware, Kosinski, and Keller, 1996). The researcher using the SF-12 can also opt to have the scoring performed online at the website of QualityMetric, Incorporated, a company founded by John Ware and associates in 1997 that develops and tests health surveys which coordinates the development and use of the SF-12 globally. According to Ware’s original description of the SF-12, test-retest reliability of the PCS-12 was 0.89 in the US and 0.86 in the UK. Coefficients of the MCS were 0.76 and 0.77 (Ware, Kosinki, and Gandek, 2002). The second version of the SF-12 has theta reliability estimates ranging from 0.73 to 0.87 across the eight scales. The value for the PCS-12 was 0.89 whereas that for the MCS-12 was 0.86 (Ware et al., 2002). In a sample of patients with arthritis, the SF-12 was compared with the SF36 (Ware, Kosinki, and Gandek, 2002). For the SF-12, intraclass reliability correlations were 0.75 compared with 0.81 for the SF-36. Furthermore, the correlation between the two scales was found to be 0.94 (Hurst, Ruta, and Kind, 1998). In another study, the correlation between the PCS scores on the two instruments was 0.95. The correlation for the MCS was 0.97 (Ware, Kosinki, and Gandek, 2002). For the PCS items, Cronbach’s alpha was 0.81 whereas it was 0.84 for the MCS items (Lim and Fisher, 1999). As for the validity of the SF-12, the PCS scores had an R2 of 0.91 while that for the MCS was 0.92. (Ware, Kosinki, and Gandek, 2002). Ware et al. (2002) also compared SF-12 scores with those of the SF-36 derived from the same data set. It was found that the correlation between the SF-12 and SF-36 PCS was 0.95 while the correlation between the SF-12 and SF-36 MCS was 0.97 (Ware, Kosinki, and Gandek, 2002). The researchers also reported that in several
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