Extreme discordant sibling pairs (EDSPs) are theoretically powerful for the mapping of
quantitative-trait loci (QTLs) in humans. EDSPs have not been used much in practice,
however, because of the need to screen very large populations to find enough pairs that are
extreme and discordant. Given appropriate statistical methods, another alternative is to use
moderately discordant sibling pairs (MDSPs)—pairs that are discordant but not at the far
extremes of the distribution. Such pairs can be powerful yet far easier to collect than extreme …

During the past few years, there has been a great deal of new work on methods for mapping
quantitative-trait loci by use of sibling pairs and sibships. There are several new methods
based on linear regression, as well as several more that are based on score statistics. In
theory, most of the new methods should be relatively robust to violations of distributional
assumptions and to selected sampling, but, in practice, there has been little evaluation of
how the methods perform on selected samples. We survey most of the new regression …