Not offering don't know options in brand image surveys contaminates data

The aims of this study were to (1) understand the extent to which offering or not offering a Don’t know option has the potential of contaminating survey data, and (2) investigate the interaction between offering a Don’t know option and the verbalisation of scale points. Results from an experimental study with 196 online panel members confirm that substantial proportions of empirical data sets can be contaminated if Don’t know options are not...