# How to rescale two questionnaires that use slightly different response scales in order to make them comparable?

I used a -4 to +4 Likert scale in one set of questionnaires and -3 to +3 for the same questionnaires, but gathered respondents in a different way. I want to rescale from -4 to +4 down to -3 to +3 for the second group.

How do I do this and secondly is there a referenced/accepted procedure for doing this?

• I am also curious, in rescaling is it easier to change '1' (slightly agree) into a '0' due primarily to '1' measuring a smaller effect than from say a '4' (totally agree) to a '3'? – hucsy Oct 1 '11 at 12:46
• I believe similar questions have been asked in the past, see How to compare Likert scales with varying number of categories across time?. – Andy W Oct 1 '11 at 13:24
• Hmm okay. Another question then. The questionnaire I used has literature to say that depending on the sample populations age and capacity, the scale can be altered to -2 too +2. This leads me to wonder then, given I am only really interested in a final value for each person (after calculating SS Stage/ SSDev x 100), do I actually need to make adjustments? Why would the author say that if it was going to impact the final value! Its been 10 years since I did stats (hence this issue) so I am struggling to find an understandable, known option. – user6613 Oct 2 '11 at 13:44
• Hi hucsy, if you register your account you should be able to edit your original question. – Andy W Oct 3 '11 at 12:19

$$X_{SCALED} = X_{ORIG} \times MAX_{SCALED}/MAX_{ORIG}$$