ptdt: Power for a TDT design

ptdtR Documentation

Power for a TDT design


Function to compute power for a TDT design using formulae from Abel and Muller-Myhsok (1998) Am J Hum Genet 63:664-667


ptdt(g, q, m, ld, nfam, alpha)



the genotype risk ratio for the susceptibility gene.


the susceptibility allele frequency


the frequency of the marker allele in linkage disequilibrium with the susceptibility allele.


the strength ofthe linkage disequilibrium between marker and susceptibility allele, on a scale of 0 to 1.


the number of families.


the significance level of the test.


We will use an R program that implements the power formulae of Abel and Muller-Myhsok (1998). These formulae allow one to quickly compute power of the TDT approach under a variety of different conditions. This R program was modeled on Martin Farrall's Mathematica notebook.

The power computations here use a simple genetic model with several aspects: (1) The disease locus has two alleles, A and a, with allele frequencies q and 1-q. The risk of disease follows a multiplicative model with genotype relative risks of g and g*g for the A/a and A/A subjects. (2) There is a perfectly linked marker with two alleles, with allele frequencies m and 1-m.



power of the statistical test under the chosen conditions.


This R program was modeled on Martin Farrall's Mathematica notebook.


Daniel E. Weeks


Abel L, Muller-Myhsok B. Maximum-likelihood expression of the transmission/disequilibrium test and power considerations. Am J Hum Genet. 1998 Aug;63(2):664-7.

Chen WM, Deng HW. A general and accurate approach for computing the statistical power of the transmission disequilibrium test for complex disease genes. Genet Epidemiol. 2001 Jul;21(1):53-67.

Iles MM. On calculating the power of a TDT study–comparison of methods. Ann Hum Genet. 2002 Jul;66(Pt 4):323-8.

Purcell S, Cherny SS, Sham PC. Genetic Power Calculator: design of linkage and association genetic mapping studies of complex traits. Bioinformatics. 2003 Jan;19(1):149-50.

See Also

plotNtdt, ntdt.q, ntdt


ptdt(q=0.15,m=0.25,ld=0.45,g=2.5,alpha = 0.05,nfam=300)
ptdt(q=0.15,m=0.25,ld=0.45,g=2.5,alpha = 0.05,nfam=400)

powerpkg documentation built on May 20, 2022, 1:09 a.m.

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