When a respondent does not answer a question this must be separated from other mission values, e.g. due to skips or when the question is not suitable for the respondent. Such cases should also be separated from answers, such as "I do not know", "I do not wish to answer", "other", etc. and from missing values because of possible subsequently added variables.
All of the mentioned examples of missing variable data must be separated from situations of missing answers for an entire unit of analysis, for which there are various reasons: a skip, a test unit, an empty unit or an incomplete unit or a partial response. In this context, special attention is also required in identifying the appropriate unit to be used in the analysis, where units that only clicked on the introduction text or only on the first question must be excluded beforehand.
Although 1KA clearly separates all of the stated categories, complex surveys still require additional attention to make sure that the correct options are selected. Default options are usually suitable when dealing with simple surveys.