Purpose
To validate the FACT-G scale for measuring quality of life of patients with cancer in Colombia.
Methods
The analysis included factor analysis, confirmatory analysis, Rasch analysis, convergent validity, internal consistency (473 patients diagnosed with cancer), test–retest reliability (97 patients evaluated at two different time points) and sensitivity to change (25 patients evaluated before and after an intervention).
Results
A four-factor structure has been found (“Physical well-being”, “Social–family well-being”, “Functional well-being” and “Emotional well-being”). Two subscales (“Emotional well-being” and “Social–family well-being”) have misfitting items. Cronbach’s alpha was 0.89 for the whole scale. None of the items had significant impact on the scale’s alpha when removed. Lin’s concordance correlation coefficient indicated test–retest reliability (rho c: 0.64–0.76) adequate to the uses of the tool. Regarding sensitivity to change, repeated measures analysis demonstrated significant change of the score after an intervention [F(3, 72) = 39.89, P = 0.000]. Except for the domain “Social–family well-being”, Pearson’s correlation coefficient between equivalent domain scores on FACT-G and the EORTC QLQC-30 ranged from 0.5 to 0.7.
Conclusions
The FACT-G scale measures a four-factor construct. Results indicate that the FACT-G scale is an instrument that performs consistently over time, with evidence of responsiveness. The finding of misfitting items in two subscales (“Social–family well-being”, and “Emotional well-being”) imposes caution in interpreting the scores of these domains.
