The meaning of the codes is as follows:
0: project variables of type v_000, except for variables that refer to text boxes: the respondent has seen the question, but has not edited it. Respondent management variables of the type “text box”: pre-filled entry where the variable has not been filled.
-66: project variables of type v_000 that refer to text boxes: the respondent has not seen the question concerned, because it was hidden.
-77: project variables of type v_000, except for variables that refer to text boxes: the respondent has not seen the question concerned, perhaps because they aborted the survey or because they were not shown the question/page due to the filter settings.
-99: project variables of type v_000 that refer to text boxes: the respondent has seen the question, but has not edited it.
In relation to text boxes, -99 indicates that a respondent has seen a question, but has not answered it.
Please note: you can set the “missing response” values within the exported data sets yourself. For more information, please refer to chapter 14.2.6 of the EFS manual.