What is the appropriate action when using poorly worded scales from previous literature?
If you change the items in a questionnaire, you have a different questionnaire. All the psychometric properties such as reliability or validity and the normative data no longer apply. You need to be able to compare your measurement to a normative sample to receive a meaningful measurement. If you change a questionnaire, you have to test it against your construct, calculate its reliability etc., and normalize it over a large representative sample. Otherwise any conclusions you draw from your experiments will be at best tentative and potentially false.

The meaning of a questionnaire item is not the literal meaning you make of that "sentence", but the relation that the behavior of answering this item has with other behavior that you know represents your construct. For example, the item "Weeds should be eradicated because they inhibit the full development of useful and ornamental plants." is from a questionnaire on environmental attitudes (Milfont &amp; Duckitt, 2004) and measures "necessity of development" (NoD). If a significant number of your sample answer "yes" to the question about weeds, and they also rate high in NoD in a valid NoD task, then this item can be used to measure NoD. If you change the words, this correlation might no longer hold.




Milfont, T. L., &amp; Duckitt, J. (2004). The structure of environmental attitudes: A first- and second-order confirmatory factor analysis. Journal of Environmental Psychology, 24, 289–303. Available online at http://gip.uniovi.es/gdiyad/docume/arti_jep01.pdf.