nsibs {powerpkg}

A function to compute power of an affected sib pair design.

Description

The nsibs() function will compute the number of affected sibpairs needed to detect linkage to a susceptibility gene attributed with a user-specified lambda sib (ls) and lambda off (lo). Lambda sib is the recurrence risk ratio for full- sibs (includes dominance variance), lambda off is the recurrence risk ratio for parent- offspring pairs (so does not include dominance variance). In these calculations we assume that parents and sibs are completely genotyped with markers that perfectly define the IBD configurations. alpha and beta correspond to the type 1 and 1 - type 2 error rates respectively.

Usage

nsibs(ls, lo, alpha, beta)

Arguments

ls

the recurrence risk ratio for full-sibs (includes dominance variance).

lo

the recurrence risk ratio for parent- offspring pairs (so does not include dominance variance)

alpha

the Type 1 error rate.

beta

one minus the Type 2 error rate, so (1-beta)=Power.

Details

In these calculations we assume that parents and sibs are completely genotyped with markers that perfectly define the IBD configurations.

Value

n

The number of sib pairs needed to obtain the desired power under the chosen study design.

Warning

Makes the simplifying assumptions that (1) all families will have exactly two affected sibpairs; and that (2) the identity-by-descent status in the ASPs can be determined unambiguously

Note

These are based on a Mathematica notebook created by Martin Farrall.

Author(s)

Daniel E. Weeks

See Also

plotNsibs, plotDom

Examples

## Use the nsibs() function to calculate the number of sibpairs required
## when lambda sib = 2 and lambda off = 2, in order to have 85 percent 
## power to detect linkage at an alpha level of 0.05.

nsibs(ls=2,lo=2,alpha=0.05,beta=0.15)