Linkage results were also found to vary when comparing the full sample to truncated samples in which varying proportions of light drinkers were dropped. Linkage that is maximal in the full sample, and drops as the sample is reduced, is consistent with the influence of genes influencing consumption in all individuals or with decreased power to detect linkage in the smaller sub-samples. In contrast, linkage that is maximal in a sub-sample, by definition, suggests the influence of genes that are expressed only in a proportion of the population. Both modes of influence were in evidence, for example, with linkage maximised in the larger samples on 1p and 6p for Quantity × Frequency and for a sub-sample on 5q for Frequency.
