I would like to know how do we analyze or regard the Neutral response (such as Don't Know) in a questionnaire using the following Likert Scale:
1:Strongly Disagree 2:Disagree 3:Don't Know 4:Agree 5: Strongly Agreee
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2 Answers
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"Don't know" is a bad neutral option, because it's not really neutral – it's barely an answer at all. If you are short on data, I suggest treating it as missing. You can then test for systematic missingness here much as you could with any other missing data. Responses that use the other four rating options are more properly ordinal, so you can equate them with ranks 1–4.
If you have a lot of data and at least a few items with this rating scale, you can try item response theory analyses. For instance, if you want to estimate a latent continuous variable using many items that have this same rating scale, a rating scale model would help you determine whether "don't know" contains any information about the latent variable at all. My guess is that it wouldn't, but if you have the data and the patience to study the methodology, you can make an empirical question and answer of it.
answered May 13, 2014 at 15:47
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$\begingroup$ Actually, the instrument I used had the "neutral" option, and it was supposed to be a validated one. I am not sure if I could have eliminated the "neutral" option and make use of only the 1, 2, 4, 5 on the scale. $\endgroup$ May 13, 2014 at 20:46
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$\begingroup$ Then you should either look for that evidence of validation or assume it's insufficient. As @Lauren and I have stated, this is not a properly neutral option, and as I've said, you can find out if it's actually associated systematically with any particular level of a latent dimensional factor, if that's what the Likert rating is supposed to indicate. Do not treat the ratings as continuous data with values 1, 2, 4, and 5 unless you have good reason to think the difference between "disagree" and "agree" is twice as large as the difference between "disagree" and "strongly disagree". $\endgroup$ May 13, 2014 at 20:52
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In general, I would recommend against including "Don't know" as the neutral option in your Likert scale. In doing that, you're not differentiating between two types of people: 1) those who really don't know or have an opinion (they may be unfamiliar with the topic, or refuse to answer), and 2) those who feel neither positively nor negatively about the subject at hand. These types of people could be very different. In fact, in a lot of surveys, people will include a neutral scale midpoint such as "Neither agree nor disagree" and also another separate option to select "Don't know" which would be treated as a nonresponse. If you want to read more about these issues I recommend looking at this resource:
Krosnick, J.A. and L.R. Fabrigar. 1997. Designing rating scales for effective measurement in surveys. In: (L. Lyberg, P. Biemer, M. Collins, E. de Leeuw, C. Dippo, N. Schwarz and D. Trewin, eds.) Survey measurement and process quality. John Wiley and Sons, Inc., New York, NY. pp. 141–164.
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$\begingroup$ I answered under the impression that the scale was already designed and the data already collected, but this is the same reasoning I had in mind. +1 for writing it out explicitly and for the reference! $\endgroup$ May 13, 2014 at 16:32