This segment is on "don't know" options.
Always a tricky question,
should you offer respondents a don't know answer
category in the questionnaire or should you not?
Howard Schuman and Stanley Presser had in
their 1981 book, "Questions and Answers in Attitude Surveys", a nice example here.
The question asked respondents on whether they are in
favor or opposed to the Agricultural Act of 1978.
The interesting thing about this question is
that this agriculture act actually didn't exist.
So, most people, as you can see in this graph here, they should say
don't know because there is no favor or opposed to something that doesn't exist.
However, in the first set of bars that you see
here, this piece here, the question was asked, just like this,
"Are you in favor or oppose?"
and there was no filtering out of people that say they have
never heard or they don't know what the Agricultural Act of 1978 is.
In this condition, we had about 70% who were volunteered the answer don't know.
In this other segment here, where first people were asked
whether they do know something about the Agricultural Act of 1978,
almost 90% said they don't and only the remaining set
was asked whether they favor or oppose this particular act.
Now there are various methods for offering don't know options.
You can have a full filter up front, "Do you
have an opinion on that?" or "Do you know about that/"
Or you can have a quasi-filter,
which is, "Do you agree, disagree, or do you not have an opinion on
that?" or "Do you favor or oppose or do you not have an opinion?"
And that would be in a formulation for a
telephone survey because in self administered mode, obviously, you
would have to write down the answer category no
opinion, even if it's not part of the questionnaire.