In Survey Solutions any question may be left unanswered for reasons beyond the control of the questionnaire designer. The respondent may refuse to answer a particular question, don’t know the answer, or a family member may be unavailable for answering.
Every once in a while our support team is receiving questions on how to designate a question “required”, so that the interview may not proceed unless this particular question is answered. The justification could be that the answer is critically important to determine subsequent trajectory through the questionnaire: eligible/non-eligible for interview, treated/controls, etc.
The requirement for the question to be answered is not the property of
that question, but rather the property of the questionnaire containing
that question. The designer of the questionnaire should decide, what
should be the consequence for the interviewing process if the question
is not answered. In most cases some further information may still be
acquired, but occasionally this would mean the end of the interview. In
that case the designer should apply the condition
as enabling (not validation) condition for all the subsequent
questions. Note that this is much easier if these questions are contained
in different sections, in which case one can apply one condition for
the whole section.