Item non-response in open-ended questions: Who does not answer on the meaning of left and right?

The left-right ideological dimension plays a central role in political science research. The meaning of left and right is often based on analyses of responses to open-ended survey questions. In the 2008 German General Social Survey, item non-response to two particular open-ended questions on the meaning of left and right was considerable and calls for analyses of the value of the data have been received. In our paper we investigate item non-response to these two open-ended questions in terms of cognitive abilities, motivational aspects, and finally, in relation to the left-right self-placement scale itself. Item non-response in the open-ended questions is not based on randomness alone, and analyses show some significant systematic results. Thus, the open-ended questions seem to be biased and the validity of this data is questionable in some respect. In this context, left-right self-placement of non-respondents and "cognitive don't knowers" need to be given careful consideration.