on the transmission of various alleles from many families, investigators can conduct statistical analyses to determine if a particular allele of the marker being tested is associated with disease development. Through the use of such a “within-family” design, the control sample of alleles is perfectly matched to the affected sample of alleles because both samples are transmitted from the same two parents. To expand the use of the TDT, researchers recently have begun to apply it to other designs, such as family-based association tests that include data from both affected and unaffected siblings or from even more extended pedigrees. In addition, the test has been extended to the analysis of quantitative traits in addition to qualitative traits.
