OSA (Ordered Subset Analysis Program ) allows the researcher to evaluate evidence for linkage even when heterogeneity is present in a data set. This is not an unusual occurrence when studying diseases of complex origin. Families are ranked by covariate values in order to test evidence for linkage among homogeneous subsets of families. Because families are ranked, a priori covariate cutpoints are not necessary. Covariates may include linkage evidence at other genes, environmental exposures, or biological trait values such as cholesterol, age at onset, and so on.
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Hauser E.R., et al.
Ordered subset analysis in genetic linkage mapping of complex traits.
Genet. Epidemiol 2004;27:53-63