World Health Organization quality of life instrument-brief and Short Form-36 in patients with coronary artery disease: do they measure similar quality of life concepts?

This study aimed to assess the validity and reliability of World Health Organization Quality of Life Instrument (WHOQOL)-brief and SF-36 in patients with coronary artery disease (CAD). Considering that depression is known to be associated with bad outcomes in CAD and it is highly associated with poor Quality of Life (QOL), we tested the correlation between WHOQOL and SF-36 and an instrument to screen depressive symptoms. It is a cross-sectional survey conducted in 103 patients with documented CAD. QOL was measured through WHOQOL-brief and SF-36 and depressive symptoms were assessed by the Beck Depression Inventory (BDI). To evaluate convergent validity, the correlations between both QOL assessment instruments were examined; discriminant validity was assessed through BDI and QOL instruments correlations. Coefficient Cronbach's alpha was used to test reliability. Percentages of floor and ceiling effects were higher in SF-36 scores than the WHOQOL-brief ones. Although WHOQOL-brief showed a maximum of 1% of floor effect and 9% of ceiling effect, SF-36 presented 40 and 32%, respectively. Internal consistency reliability ranged from 0.65 to 0.85 for the WHOQOL-brief and 0.57 to 0.89 for the SF-36. Correlations between subscales of WHOQOL-brief and BDI ranged from -0.74 to -0.61 and correlations between subscales of SF-36 and BDI ranged from -0.68 to -0.26. SF-36 and WHOQOL-brief seem to be valid and consistent QOL measures in patients with CAD. Researchers should define the aims of their studies before choosing which instrument to use, because they appear to measure different constructs of QOL.