Visual analogue scales for mode-independent measurement in self-administered questionnaires.

Previous research has shown evidence for mode differences between computer-assisted self-administered interviews (CASI) and paper-and-pencil interviews, especially in the case of sensitive questions. Some of these differences are explained by higher degrees of self-disclosure for CASI than for paper-and-pencil interviews, due to the more private situation with CASIs. This analysis examines the existence of different degrees of self-disclosure for CASI versus paper-and-pencil questionnaires and whether these differences can be reduced by the use of a specific response format. Judgments of items on a self-control scale with discrete 5-point (Likert-type) scales are compared with judgments on continuous visual analogue scales (VAS). Because a categorization effect for Likert-type items is assumed when pressure for social desirability is present, it is hypothesized that VAS compared to Likert-type response formats are less sensitive to mode differences.