You can add an N/A (not applicable) column to any question type that uses weights:
When respondents select the N/A answer option, that answer will not be factored into the question's weighted average calculations in the Analyze Results section.
To add an N/A column to a Matrix/Rating Scale or Ranking question:
When you add an N/A column to a Matrix/Rating Scale question (with the Use Weights option applied), an N/A column without a weight associated with it will be added to the column choices.
If a rating item does not apply to a respondent, an N/A column will give the respondent an opportunity to essentially opt out of the question, instead of choosing an inaccurate answer.
When you add an N/A option to a Ranking question, it will add an N/A checkbox at the end of each row. If a respondent selects an N/A checkbox, that row will be greyed out and will not be included in that respondent's ranking order.
Respondents answer a Ranking question by dragging and dropping their answers in order of preference, so you want to make sure that even the lowest ranked options still apply to that respondent. If a respondent doesn't have the option to declare that a ranking item does not apply to them, they will be forced to include that choice in their rankings anyway, which might produce bad data.
You can also add an N/A option as an additional answer choice to other question types, like Multiple Choice, but the system will not automatically remove those choices from analysis.
To learn more about the pros and cons of the N/A answer choice, take a look at our blog post here: The N/A Answer Choice: When It’s Good To Use & When It’s Not (English only).