We propose here a method of inferring the effects of an unmeasured genetic variant (such as DRB1*04) using linkage disequilibrium (LD) measures from an independent reference data set (the British 1958 Birth Cohort) to scale and weight the associations of rheumatoid arthritis with tagSNPs in the North American Rheumatoid Arthritis Consortium (NARAC) data set, supplied as Problem 1 for the Genetic Analysis Workshop 16. Here, HLA-DRB1 is linked to rheumatoid arthritis.