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Within Turkey, Korea and the UK, the 14 items can be summated to give an index of disease activity. Analysis of the pooled data confirmed that the index is not suitable for comparison between countries or for pooling of data in the raw form, but after fitting the data to the Rasch model such comparisons can be made. This gives a scaling tool that is quick and easy to use in the clinical situation.
Gemma Lawton (Wed,) studied this question.