Equine disease association studies: a clinician's perspective

Diagnostic criteria should be carefully defined and described in disease association studies to allow (1) comparison among studies from different laboratories evaluating the same disease, (2) critical evaluation of selection procedures of patients, and (3) to strengthen genuine associations with any genetic marker system. Factors to consider include age at onset of disease, specialized diagnostic methods necessary to diagnose or eliminate patients with a selected disease, ranges of affectedness and differences in sex expression.