Frederik Funke & Ulf-Dietrich Reips (2012).
Why semantic differentials in Web-based research should be made from visual analogue scales and not from 5-point scales

Field Methods, 24, 310–327. doi:10.1177/1525822X12444061

In a Web experiment, participants were randomly assigned to 2 semantic differentials either made from discrete 5-point ordinal rating scales or from continuous visual analogue scales (VASs) with 250 gradations. Respondents adjusted their ratings with VASs more often to maximize the precision of answers, which had a beneficial effect on data quality. No side effects like differences in means, higher dropout, more nonresponse, or higher response times were observed. Overall, the combination of semantic differentials and VASs results in a number of advantages. Potential for further research is discussed.