Subjective health status assessment: evaluation of the Italian version of the SF-12 Health Survey. Results from the MiOS Project.

BACKGROUND SF-12 is a generic short form health survey, developed in the USA from the original SF-36. It produces two summary measures evaluating physical and mental self-perceived health that are interchangeable with those from the SF-36. SF-12 has been successfully tested in nine Western European countries on large samples of the general population, where it has proved its brevity, comprehensiveness, reliability, validity and cross-cultural applicability. The present analysis directly assesses the SF-12 for the first time in various Italian settings, including the general population and specific patient groups. METHODS Data for this report were collected from five different samples; in four of them the SF-12 was used as a 'stand-alone' instrument, while in the other one (used as the reference) it was embedded in the SF-36. Descriptive statistics, Spearman's correlation coefficients, confirmatory factor analysis, ordinal uni- and multi-variate least squares regression model and covariance analysis were used to evaluate the summary measures in each sample, and across relevant subgroups. Studies were ordered according to the expected deviance, from the 'normal' health status of the reference group to the sample with the expected highest level of illness. RESULTS Overall, more than 11,000 subjects were evaluated. Response rates ranged from 63 to 100%, while missing items accounted only for 0.2-8.2% of all items. Uni- and multi-variate analyses showed a positive association between both physical component summary (PCS) and mental component summary (MCS) scores and their respective items in all examined samples. MCS scores were fairly similar across all samples, with the only exception being patients recently discharged from hospital, whose subjective mental health perception was higher than expected and the highest of all (52.2). Finally, we found a substantial impact of ageing on physical health perception, while the MCS was shown to be less sensitive to the age effect. CONCLUSIONS This analysis shows that the SF-12 has good validity, while some issues related to its most appropriate mode of administration and target groups might require further attention.