Validity and reliability of the Brazilian version of the Work Ability Index questionnaire.

OBJECTIVE To evaluate the validity and reliability of the Portuguese language version of a work ability index. METHODS Cross sectional survey of a sample of 475 workers from an electrical company in the state of Sao Paulo, Southeastern Brazil (spread across ten municipalities in the Campinas area), carried out in 2005. The following aspects of the Brazilian version of the Work Ability Index were evaluated: construct validity, using factorial exploratory analysis, and discriminant capacity, by comparing mean Work Ability Index scores in two groups with different absenteeism levels; criterion validity, by determining the correlation between self-reported health and Work Ability Index score; and reliability, using Cronbach's alpha to determine the internal consistency of the questionnaire. RESULTS Factorial analysis indicated three factors in the work ability construct: issues pertaining to 'mental resources' (20.6% of the variance), self-perceived work ability (18.9% of the variance), and presence of diseases and health-related limitations (18.4% of the variance). The index was capable of discriminating workers according to levels of absenteeism, identifying a significantly lower (p<0.0001) mean score among subjects with high absenteeism (37.2 points) when compared to those with low absenteeism (42.3 points). Criterion validity analysis showed a correlation between the index and all dimensions of health status analyzed (p<0.0001). Reliability of the index was high, with a Cronbach's alpha of 0.72. CONCLUSIONS The Brazilian version of the Work Ability Index showed satisfactory psychometric properties with respect to construct validity, thus constituting an appropriate option for evaluating work ability in both individual and population-based settings.