Five items are sufficient to assess rheumatoid arthritis disease activity by patient reported outcome measure: a computer adaptive test simulation study

Disease Activity (DA) monitoring is a standard of care in RA. Rasch measurement theory analyses of legacy RA DA patient reported outcome measures (PROMs) was used to develop a valid item pool of 12 items, covering five domains: Tenderness and swelling, Disease activity, Pain, Stiffness, and Physical functioning. The aim of this study was to determine whether it could be advantageous to administer these 12 RA DA items via a computer adaptive test (CAT).

Simulations were conducted to assess whether the 12 RA items would cover all five domains adequately. Two sets of simulations were run with stopping rules equivalent to Cronbach's α values of 0.70 and 0.85, respectively. Further CAT simulations would have been run, if coverage of the five domains were inadequate, based on the statistical information and measurement range of the items.

In both sets of initial simulations, stopping rules were most commonly satisfied after the administration of five items. However, these five items only covered three domains, with the Disease activity domain consistently missed. Two sets of five items were generated, with summary measures (maximum and mean standard error) equivalent to the initial simulations.

In the context of the simulations undertaken here, a CAT does not provide any major advantage for the purposes of administering the 12 RA DA items of the item pool in comparison to administering one item from each of the five domains, and administering one item from each of the five domains appears to be sufficient. We therefore propose the development of a brief, simple to administer, and psychometrically evidenced PROM for the assessment of RA DA.