Survey Solutions recognizes two situations of missingness:
- the value is missing because the logic of the questionnaire is disabling (skipping) this question. There is nothing that the interviewer can do to enter a value in such a field and in some cases even to see the question and its options.
- the value is missing despite the question is enabled (not skipped). This could be because of any of the following:
- interviewer hasn't reached this point in the interview;
- interviewer missed the question, didn't ask it and hence no answer was recorded;
- none of the options was suitable to accommodate the respondent's answer and hence the interviewer didn't record the answer;
- other similar situations.
In the first case the missingness will be reflected in the export data file with a system missing, in the second case special reserved values will be used:
- for numeric variables, the value: -999,999,999;
- for string variables, the value: ##N/A##.
These special values should be replaced with proper missing values prior to performing the analysis.