Out of 2300 patients with rheumatic diseases 1627 were analysed to develop
a classification of rheumatoid arthritis based on clinical attributes of pa
in. Of these, 641 patients had the disease and 986 were controls with other
rheumatic conditions. For traditional format classification, six of eight
variables were selected: pain at a fixed joint; symmetrical pain; continuou
s pain; pain mainly present at night or in the morning; pain following join
t pressure; and pain decreased by load/movement. The occurrence of four or
more of these features was associated with a 72.1% sensitivity and a 79.1%
specificity. A classification tree constructed on four features that showed
the greatest diagnostic power (symmetrical pain, pain mainly present at ni
ght or in the morning, pain at joint pressure, continuous pain), was associ
ated with a 75.8% sensitivity and a 77.0% specificity.