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 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)

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)

If any SF-12 component item is missing, MCS 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.

AHRQ documentation notes that negative values are possible in rare cases. One case in the 2016 FYC data has a negative value.

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.