Ruperto N et al. - We describe these techniques, how they work, and their practical application in pediatric rheumatology, where they have been widely used to develop the outcome measures of several chronic rheumatic diseases, including juvenile idiopathic arthritis, rheumatoid arthritis, systemic lupus erythematosus, and idiopathic inflammatory myopathies, as well as the classification criteria for juvenile systemic sclerosis and juvenile vasculitides.