At no other time in the history of multiple sclerosis (MS) has the accurate measurement of health outcomes been so important. There are now many kinds of interventions of proven or potential efficacy available for people with MS and many other methods are under investigation. Not all outcomes that matter can be measured with a biological parameter. Many important outcomes of treatment can be assessed only by asking the patient directly. For clinical decision making, asking one good question, asking it consistently, and writing down the answer will produce historically accurate data to judge MS progression on life-altering constructs like fatigue, depression and pain. To get a total score from items in a questionnaire, Rasch Measurement Theory provides a way of estimating the extent to which the items form a linear continuum with mathematical properties. Preference-based measures, when the preferences are derived from patients, permit the impact of the multiple health dimensions associated with MS to be valued. The bottom line is, ask a good question and you will likely get a good answer, ask a poor question and assuredly, you will not.
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