For some questions, the respondent is simply asked to mark an oval if it is appropriate. Leaving it blank is a valid answer (not a skipped question). For example, many questions on the DHQ ask the respondent to "mark as many as apply". For each oval, "1" is typically used to indicate "filled in" and "0" is used to code "left blank." However, alternative codes can be used (see General Formats on the Settings menu of Diet*Calc's dictionary editor).
Missing and error codes do not apply to this format.