Don’t know about don’t know
Should I include “I don’t know” in a questionnaire?
Good question, this is one that people often get wrong – either because they forget to consider it or they don’t think it through. The concern would be that if you show a respondent a ‘don’t know’ response option they will feel compelled to select it instead of giving a ‘real’ answer. Maybe it will put the idea in their head, or maybe it will allow them to be lazy and avoid thinking about their genuine answer. Fair enough, we want to avoid that.
Well, glad to be of service. The answer is… er… don’t know.
The problem with this is that it depends on the context and as I often say questionnaire design is all about being human and thinking about your respondent and how they might approach each question. The ultimate aim is always to allow the respondent to give the answer that is true to them.
When it comes to ‘don’t know’ there are four types of questions where the solution is straightforward:
1. The bleeding obvious. Solution: Do not include Don’t know
Example: Do you own a car?
Example: Did you have breakfast today?
Example: Would you like a free bar of chocolate?
Recent behaviour questions tend to be straightforward. Something happened, and people remember it. Questions relating to unimportant decisions are also easy for people to answer. You should be able to reasonably expect anyone to say either yes or no to a question like this. Don’t know really would not be required.
2. The ethical quandary. Solution: Include Don’t know
Example: Should the UK increase the school leaving age to 18?
Example: Which diseases should the NHS prioritise for treatment?
Example: Should prisoners be allowed to vote?
Attitude questions can be complicated. An attitude question may be a bit of a moral dilemma, and you may not be sure where you stand on it. You might have thought long and hard, and have thoughts on the pros and cons, and still be unsure or unwilling to come down on either side. Your final answer to this question could be don’t know, so you should be able to say so.
3. The genuine unknown. Solution: Include Don’t know
Example: Did your mother buy any margarine in the last week?
Example: What brand of dusters do you buy?
Example: How many biros do you use each year?
On matters mundane, improbable or relating to the opinions or behaviour of others, there are circumstances where you probably wouldn’t be able to give an answer that you were certain about. You probably don’t know, so you should be able to say so.
4. The forced answer. Solution: Do not include Don’t know
Example: Would you like to enter our prize draw?
Example: Did you look at our website?
Example: Are you vegetarian?
Sometimes, for research purposes, you need the respondent to pick one answer or the other – usually for purposes of screening or routing people into question sets that apply to them.
In all other cases that do not fall under these four types, well meh – it’s up to you. Weigh up how your respondent might approach the question against how much it matters to you that they don’t pick the DK option, and do what feels right in each case.
There is another wee trick you can use though, but it only works in interviewer administered (face-to-face or telephone) surveys.
Don’t Know [DO NOT READ OUT]
You can put don’t know in there as an option for the interviewer to check if the respondent insists that don’t know is their final answer. Doesn’t work in a self completion survey though unfortunately, as you can’t hide it in the same way.
While we’re at it, don’t forget don’t know’s little friends:
- Not applicable
- Can’t remember
- Prefer not to say