In a questionnaire-based study, where most questions are followed with a Likert scale from 1 to 5, how would you present your findings for responses to the item "do not know"? In some questions, the majority of responses are "do not know", how this will affect the statistical measurements? Should we ignore these responses or add them? If we add them what would be the meaning of the mean for the study?
Hello Samy,
A lot of survey researchers would code "Do not know" responses as a separate category, just as they would "Refuse to answer." The reason is, the people who give this response may be systematically different from those who do not with respect to their status on that and other variables of interest.
The confusion starts, in my opinion, when designers include "Do not know" as a middle category in Likert-type response scales. Words have meaning, and, semantically, "Do not know" may be interpreted by respondents quite differently than alternatives such as "Neutral," or "Neither agree nor disagree." For this reason, "Do not know" is not a really good choice, unless you are trying to segregate cases who are ignorant of a topic (as in the first paragraph). As well, some folks avoid neutral categories altogether in their response scales (though doing so makes the item a forced-choice item, which can yield some technical concerns, covered under the topic of ipsative scores).
Good luck with your work!
If the option is inserted as part of the Likert Scale score and if the scale is validated, you may need to refer to the literature on the scoring methods and to determine the cut-offs for categorization. However, in such cases, you may tabulate the score and analyze them as a continuous score outcome. This will give more power to your statistical results rather that categorization. Usually such option will be in the middle of the scale, and you can't remove the response option to yield your total score of the scale.
For a five-point Likert scale of questionnaire, it usually contains strongly agree, agree, neutral (some use neither agree or disagree), disagree and strongly disagree as response options (or vice-versa). Thus, try not to use "Do not know" to conform what normal questionnaires use. If possible, try not use such ambiguous response option.
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