Since relationships will be unknown in most case-control studies, it is useful to consider approaches that do not depend on the existence of known relationships. Genetic relatedness among individuals can be estimated if genetic markers are available. Under the assumption that the loci are unlinked, several methods for estimating relatedness have been developed including traditional maximum-likelihood estimation [Thompson, 1975] and other estimators based on method-of moments approaches [Ritland, 1996; Lynch and Ritland, 1999; Wang, 2002]. Compared to other estimators, maximum-likelihood estimators of relatedness exhibit the desirable features of having consistently lower standard errors and being adaptable to many sampling situations [Milligan, 2003; Thompson, 1975].
