Objective. Trials of rheumatoid arthritis (RA) treatments report the average response in multiple outcome measures for treated patients. It is more clinically relevant to test whether individual patients improve with treatment, and this identifies a single primary efficacy measure. Multiple definitions of improvement are currently in use in different trials. The goal of this study was to promulgate a single definition for use in RA trials. Methods. Using the American College of Rheumatology (ACR) core set of outcome measures for RA trials, we tested 40 different definitions of improvement, using a 3‐step process. First, we performed a survey of rheumatologists, using actual patient cases from trials, to evaluate which definitions corresponded best to rheumatologists' impressions of improvement, eliminating most candidate definitions of improvement. Second, we tested 20 remaining definitions to determine which maximally discriminated effective treatment from placebo treatment and also minimized placebo response rates. With 8 candidate definitions of improvement remaining, we tested to see which were easiest to use and were best in accord with rheumatologists' impressions of improvement. Results. The following definition of improvement was selected: 20% improvement in tender and swollen joint counts and 20% improvement in 3 of the 5 remaining ACR core set measures: patient and physician global assessments, pain, disability, and an acutephase reactant. Additional validation of this definition was carried out in a comparative trial, and the results suggest that the definition is statistically powerful and does not identify a large percentage of placebo‐treated patients as being improved. Conclusion. We present a definition of improvement which we hope will be used widely in RA trials.

Criteria for the classification of Takayasu arteritis were developed by comparing 63 patients who had this disease with 744 control patients with other forms of vasculitis. Six criteria were selected for the traditional format elass$cation: onset at age 1 4 0 years, claudication of an extremity, decreased brachial artery pulse, >10 mm Hg difference in systolic blood pressure between arms, a bruit over the subclavian arteries or the aorta, and arteriographic evidence of narrowing or occlusion of the entire aorta, its primary branches, or large arteries in the proximal upper or lower extremities. The presence of 3 or more of these 6 criteria demonstrated a sensitivity of 90.5% and a specificity of 97.8%. A classification tree also was constructed with 5 of these 6 criteria, omitting claudication of an extremity. The classification tree demonstrated a sensitivity of 92.1% and a specificity of 97.0%.

Criteria for the classification of giant cell (temporal) arteritis were developed by comparing 214 patients who had this disease with 593 patients with other forms of vasculitis. For the traditional format classification, 5 criteria were selected: age 1 5 0 years at disease onset, new onset of localized headache, temporal artery tenderness or decreased temporal artery pulse, elevated erythrocyte sedimentation rate (Westergren) 2 5 0 mml hour, and biopsy sample including an artery, showing necrotizing arteritis, characterized by a predominance of mononuclear cell infiltrates or a granulomatous process with multinucleated giant cells. The presence of 3 or more of these 5 criteria was associated with a sensitivity of 93.5% and a specificity of 91.2%. A classijication tree was also constructed using 6 criteria. These criteria were the same as for the traditional format, except that elevated erythrocyte sedimentation rate was excluded, and 2 other variables were included: scalp tenderness and claudication of the jaw or tongue or on deglutition. The classification tree was associated with a sensitivity of 95.3% and specificity of 90.7%.

Criteria for the classification of Churg-Strauss syndrome (CSS) were developed by comparing 20 patients who had this diagnosis with 787 control patients with other forms of vasculitis. For the traditional format classification, 6 criteria were selected: asthma, eosinophilia >lo% on differential white blood cell count, mononeuropathy (including multiplex) or polyneuropathy, non-fixed pulmonary infiltrates on roentgenography, paranasal sinus abnormality, and biopsy containing a blood vessel with extravascular eosinophils. The presence of 4 or more of these 6 criteria yielded a sensitivity of 85% and a specificity of 99.7%. A classijication tree was also constructed with 3 selected criteria: asthma, eosinophilia > 10% on differential white blood cell count, and history of documented

Objective. To develop a set of disease activity measures for use in rheumatoid arthritis (RA) clinical trials, as well as to recommend specific methods for assessing each outcome measure. This is not intended to be a restrictive list, but rather, a core set of measures that should be included in all trials. Methods. We evaluated disease activity measures commonly used in RA trials, to determine which measures best met each of 5 types of validity: construct, face, content, criterion, and discriminant. The evaluation consisted of an initial structured review of the literature on the validity of measures, with an analysis of data obtained from clinical trials to fill in gaps in this literature. A committee of experts in clinical trials, health services research, and biostatistics reviewed the validity data. A nominal group process method was used to reach consensus on a core set of disease activity measures. This set was then reviewed and finalized at an international conference on outcome measures for RA clinical trials. The committee also selected specific ways to assess each outcome. Results. The core set of disease activity measures consists of a tender joint count, swollen joint count, patient's assessment of pain, patient's and physician's global assessments of disease activity, patient's assessment of physical function, and laboratory evaluation of 1 acute‐phase reactant. Together, these measures sample the broad range of improvement in RA (have content validity), and all are at least moderately sensitive to change (have discriminant validity). Many of them predict other important long‐term outcomes in RA, including physical disability, radiographic damage, and death. Other disease activity measures frequently used in clinical trials were not chosen for any one of several reasons, including insensitivity to change or duplication of information provided by one of the core measures (e.g., tender joint score and tender joint count) The committee also proposes specific ways of measuring each outcome. Conclusion. We propose a core set of outcome measures for RA clinical trials. We hope this will decrease the number of outcomes assessed and standardize outcomes assessments. Further, we hope that these measures will be found useful in long‐term studies.