Response categories are developed for questions in
order to facilitate the process of coding and analysis.
Many studies have looked at the effects of presenting a
"don't know" option in attitudinal questions.
The "don't know" option allows respondents to
state that they have no opinion or have not thought about
a particular issue.
The physical placement of the "undecided"
category (at the midpoint of the scale, or separated from
the scale) can change response patterns. Respondents are
more likely to choose the "undecided" category
when it was off to the side of the scale. There are also
different response patterns depending on whether the
midpoint is labeled "undecided" or
Several researchers have found that the physical
location of the middle alternative can make a difference
in responses, and that placing the middle option at the
last position in the question increases the percentage of
respondents who select it by over 9 percent. Frequently,
offering respondents a middle alternative in a survey
question will make a difference in the conclusions that
would be drawn from the data. The middle option of an
attitudinal scale attracts a substantial number of
respondents who might be unsure of their opinion.
Researcher have also studied the "don't
know" option for factual questions. Unlike attitude
questions, respondents might legitimately not know the
answer to a factual question. Surprisingly, the research
suggests that the "don't know" option should
not be included in factual questions. Questions that
exclude the "don't know" option produce a
greater volume of accurate data. Furthermore, there is
generally no difference in response rate depending on the
inclusion or exclusion of the "don't know"
option. There is still a controversy surrounding the
"don't know" response category. Many
researchers advocate including a "don't know"
response category when there is any possibility that the
respondent may not know the answer to a question. The
best advice is probably to use a "don't know"
option for factual questions, but not for attitude