On the power of affected relative pair designs for linkage studies

Using the recurrence risk ratio (lambda), Risch (1990b) indicated that affected pairs of distant relatives are preferable to affected sib-pairs for linkage analysis when lambda is large and the mode of inheritance is additive. By using the optimum test for affected sib-pairs instead of the test used by Risch (1990b), the range of values of lambda for which the affected sib-pair design has larger or smaller power than other pairs is clarified. Risch's conclusion remains true when lambdaO > 2.5, however, sib-pairs have larger power for lower values. As affected sib-pairs occur smore frequently than other relative pairs, when ascertainment costs are non-negligible, they may be the most cost-effective relative pairs to use.