Figure 2.

Information content for two typical physical-function items. The figures indicate that rewritten items (dashed lines) have improved information content compared with their Legacy counterparts (solid lines). Item information is a function of the area under the curve. A theta of zero represents the population mean (x-axis). Each integer is one standard deviation above or below the mean. More-severe illness is represented by points to the left of zero.

Bruce et al. Arthritis Research & Therapy 2009 11:R191   doi:10.1186/ar2890
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