A Comparison of Two Methods of Measuring Oral-health-related Quality of Life of Edentulous Patients: Visual Analogue vs. Likert Scale

Researchers need to know which response options for self-administered questionnaires are most reliable and discriminatory. Objectives: To determine the association between a categorical frequency response option and a linear intensity method of response to the same oral health related quality of life questionnaire, the Oral Health Impact Profile (OHIP). Methods: In a randomised clinical trial, two OHIP questionnaires, one using a 6 point Likert-type response format, and another with 100mm visual analogue scales (VAS) were completed by subjects who received mandibular two implant supported overdentures (N=47) and conventional dentures (N=50) at two months post treatment. The Likert scale included categories that ranged from 0 for problems that occur all of the time to 5 if the problem never occurred. The VAS were anchored with 0 for completely dissatisfied to 100 for completely satisfied. To compare the two forms, the Likert scores were converted into percentages by multiplying each item response by 20. Results: There was a significant relationship between the two forms (r ranged from 0.75 to 0.9, P<0.01) for all seven domains of the OHIP (functional limitations, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap), With both forms, it was found that participants in the implant group had significantly less problems than those in the conventional group on all seven domains of the OHIP (t-test, P<0.05). However,the differences were slightly larger with the VAS than with the Likert scale. Conclusions: In this study, the two methods of measuring response options are comparable. The Likert scale is easier to use, while the VAS is more sensitive. Choice should depend on the size of the population and of the expected between-group differences. This work was funded by the Canadian Medical Research Council, and the Fonds de recherché en santé du Québec.