This is a UK based group of lupus experts led by Prof David Isenberg that has been studying how disease activity can be accurately measured in clinical practice and also in clinical trials. This has been a long process of evolution, constantly refining the measures we use to quantify disease activity. The BILAG group is also a very  cohesive group of lupus clinicians that has collaborated on many other studies.

References

Isenberg DA, Allen E, Farewell V, D'Cruz D, Alarcón GS, Aranow C, Bruce IN, Dooley MA, Fortin PR, Ginzler EM, Gladman DD, Hanly JG, Inanc M, Kalunian K, Khamashta M, Merrill JT, Nived O, Petri M, Ramsey-Goldman R, Sturfelt G, Urowitz M, Wallace DJ, Gordon C, Rahman A. An assessment of disease flare in patients with systemic lupus erythematosus: a comparison of BILAG 2004 and the flare version of SELENA. Ann Rheum Dis. 2011;70:54-9. 
 
Yee CS, Cresswell L, Farewell V, Rahman A, Teh LS, Griffiths B, Bruce IN, Ahmad Y, Prabu A, Akil M, McHugh N, D'Cruz D, Khamashta MA, Isenberg DA, Gordon C. Numerical scoring for the BILAG-2004 index. Rheumatology (Oxford). 2010;49:1665-9.

McElhone K, Castelino M, Abbott J, Bruce IN, Ahmad Y, Shelmerdine J, Peers K, Isenberg D, Ferenkeh-Koroma A, Griffiths B, Akil M, Maddison P, Gordon C, Teh LS. The LupusQoL and associations with demographics and clinical measurements in patients with systemic lupus erythematosus. J Rheumatol. 2010;37:2273-9.