The power of the N-test of haplotype concordance

The N-test of haplotype concordance among siblings affected by some disease under investigation is used to decide whether there is a disease susceptibility gene linked to a marker locus or chromosomal region. The use of this test and appropriate modifications of it is briefly reviewed. The power of the ordinary N-test is then derived as a function of several parameters. The sample size needed to attain a given power is then derived. Some of the parameters are specified and the required sample sizes are given in tables for different values of the main unknown parameters.