The SF-12 asks questions about general health, limitations in a typical day, and limitations in the past 4 weeks. Analysis of SF-12 data relies on two summary scores: the Mental Component Summary (MCS) and the Physical Component Summary (PCS). Each summary variable includes all 12 items, but weights different items more heavily.

The PCS puts more emphasis on:

• During a typical day, limitations in moderate activities (ADDAYA)

• During a typical day, limitations in climbing several flights of stairs (ADCLIM)

• During past 4 weeks, pain interfered with normal work outside the home and housework (ADPAIN)

• During past 4 weeks, as result of physical health, accomplished less than would like (ADPALS)

• During past 4 weeks, as result of physical health, limited in kind of work or other activities (ADPWLM)

The MCS puts more emphasis on:

• During the past 4 weeks, felt downhearted and blue (ADDOWN)

• During the past 4 weeks, felt calm and peaceful (ADCAPE)

• During the past 4 weeks, as a result of mental problems, accomplished less than you would like (ADMALS)

• During the past 4 weeks, as a result of mental problems, limited in kind of work or other activities (ADMWLM)

• During the past 4 weeks, physical health or emotional problems interfered with social activities (ADSOCA)

If any SF-12 component item is missing, PCS cannot be computed directly, though a proprietary method for computing the scores is available from QualityMetric, Inc. Scores are calculated according to the standard algorithm and incorporate imputations for some cases with missing data; negative values are possible in rare cases. The variable SFFLAG indicates if the scores were imputed; though cases were not imputed if too much of the component information was missing.

For more information, the key reference for the SF-12 is

Ware, J.E., Kosinski, M., and Keller, S.D. (1996). A 12-item short-form health survey: Construction of scales and preliminary tests of reliability and validity. Medical Care 34:220.

Comparability of the raw scores between 2000-2002 and 2003 and later years is affected by a change to using SF-12 version 2 in 2003 from using SF-12 version 1 in earlier years. The PCS and MCS scores based on Version 1 of the SF-12 in these three years were based on norms from 1990, whereas SF-12 version 2 scores based on Version 2 of the SF-12 were based on norms from a 1998 national study.

To appropriately compare Version 1 with Version 2 scores, Version 1 scores need to be rescaled to 1998 norms. This can be done by adding 1.07897 to PCS scores from Version 1, and by subtracting 0.16934 from Version 1 MCS scores.