However, this pattern could arise from difficulty in coping with hip OA, rather than a higher incidence of the disease. Self-employed farmers with hip disease might seek joint replacement more readily than other workers(referral bias), as the necessity of continuing in physically arduous work could be greater, the options for alternative deployment more limited. In Sweden, where a disability pension is available to farmers with hip OA, a particularly high rate of award [Odds ratio (OR) = 13.8, 95% confidence interval (CI) = 4.0-48.1] was found relative to physically less demanding occupations and this too might arise from self-selection rather than a higher incidence of disease.