What should be the cut point for classification criteria for studies in gout? A conjoint analysis

Abstract

Objective To determine the acceptable level of positive predictive value (PPV) and negative predictive value (NPV) for classification criteria for gout, given the type of study. Methods We conducted an international web-based survey with 91 general practitioners and rheumatologists, experienced in gout. Conjoint analysis was used as the framework for designing and analyzing pairs of two profiles each describing a study type, a PPV and NPV. There were 5 study types presented: a phase 3 RCT of an NSAID versus prednisone for acute gout flares; a phase 3 RCT of a biologic agent for acute gout flares; a phase 2 RCT of a novel uricosuric drug of unknown efficacy and limited toxicity data; a case-control genome-wide-association (GWAS) study of gout; a cohort study examining long term outcomes of gout. PPV and NPV both had five levels ranging from 60-99%. Results The panellists in majority were male (65%) rheumatologists (93%) with an average of 19 years of practice seeing 5 to 60 patients with gout monthly. PPV was most highly weighted in decision making: the relative importance was 59% for PPV; 29% for NPV and 13% for study type. The preferred PPV was 90% or 80%, with an accompanying NPV of 70% or 80%, dependent on study type. Conclusion Preferred positive predictive values and negative predictive values range between 70% and 90% and differ by study type. A single cut-point can be a reasonable approach for all study types if a PPV of 90% and NPV of 80% is approximated. This article is protected by copyright. All rights reserved.