The Comparison of Likert-Type Scale and Visual Analogue Scale for the assessment of Quality of Life: eliability, Validity and Measurement Invariance

Likert-Type Scale and Visual Analogue Scale (VAS) are two common psychometrical methodologies for measuring Quality of Life (QOL). However, these two scales are different from their constructions and rating methods. Besides, whether these different attributes will result in different psychometric properties for Likert-Type Scale and VAS on measuring QOL has not yet been examined. Thus in this present study, the author has compared Likert-Type Scale and VAS for measuring QOL in three aspects: (1) the degree of agreement between these two scales, (2) the evaluation of the Measurement Equivalence/Invariance (ME/I) over these two scales for the assessment of QOL, and (3) the investigation of construct validity of theoretical framework of QOL across these two scales. 496 adult subjects were used in the current study (58.9% female, n= 292; 40.2% male, n=200; mean age=24.64 yrs). Each subject was asked to fill in the WHOQOL-BREF in two different visions, one was measured by Likert-type scale and the other was by VAS. Reliability analyses were applied by using Cronbach’s alpha coefficient and split-half coefficient. Besides, agreement analyses were applied by using Pearson’s r, Intraclass Correlation Coefficient (ICC), Lin’s Concordance Correlation Coefficient (CCC), and Bland-Altman Plot. Finally, a MTMM matrix and Confirmatory Factor Analysis (CFA) were used to examine the validity and ME/I across Likert-type Scale and VAS. The result indicated that both Liker-Type Scale and VAS are easy for subjects to answer, and possessed adequate reliability, although reliability for VAS measures are consistently higher than for Likert-Type measures. The agreements between these two scales were high, indicating adequate reproducibility of test scores across the scales. In ME/I analyses, the result showed that VAS measures and Likert-Type measures did not reflect the same structure; furthermore, the VAS defined a better construct of QOL. In a word, VAS seemed to have better psychometric properties for measuring QOL over Likert-Type Scale. But according to the characteristics of subjects in the current study, the result will be applied to healthy and well-educated subjects, and the generalization on special populations (i.e., elderly and patients) is remained to be further explored.