Measuring people's knowledge about vaccination: developing a one-dimensional scale.

We propose a new scale to measure people's general knowledge about vaccinations. The scale's psychometric properties and its relationship with people's willingness to vaccinate were examined in two studies. In Study 1, a representative sample of the German- and French-speaking populations in Switzerland (N=1123) responded to a mail survey. In Study 2, members of an online panel answered the same questions (N=233). The results of both studies suggest that people differ considerably in their ability to correctly answer questions related to vaccinations. Mokken scale analyses and a test-retest analysis showed that nine items form a one-dimensional scale with good psychometric properties. In both studies, a substantial correlation between knowledge and willingness to vaccinate was observed. The scale proposed in this study is well suited for research examining group differences. In a time when new media such as the Internet is highly accessible to most people, misconceptions can easily be spread. A good knowledge scale is important for measuring possible knowledge changes.