To test the reliability of two radiologic scoring methods in rheumatoid arthritis (RA)--the Sharp/van der Heijde (SvH) and the Larsen/Scott (LS)--with generalizability analyses.
Films of 51 patients representing the spectrum of early RA were read by two raters for each method. The discriminative ability and responsiveness were expressed as: intraclass correlation coefficients (ICCs), two types of smallest detectable difference (SDD), and two types of smallest detectable change (SDC); reflecting measurement error when discriminating between or detecting changes within (1) individuals or (2) groups. They were calculated for (average) scores of one to three raters.
The discriminative capacity (0.85-0.97) and responsiveness (0.91-0.97) were good when expressed by ICC. On the group level the SDDs and SDCs ranged between 0.6-3.3% of the max. obtainable score. On the individual level, the scores showed better reliability measured with the SvH (SDDs 2.0-3.4%) than with the LS (SDDs 5.3-9.2%). The SvH also assessed changes in scores in individuals with less measurement error (SDCs 1.3-2.2%) than the LS (SDCs 2.3-3.9%).
For early RA patients, the SvH seems preferable if analyses on individual level are included.