effects, however, so a more practical approach is to consider the ranks of test statistics of the true effects [24]. Here, it is shown that similar information to the one-stage design is obtained by genotyping all markers on 50 per cent of the sample and then genotyping the 10 per cent most promising on the remainder, resulting in a decrease of about 45 per cent in the number of genotypes. Again, the total sample size can be calculated for a one-stage design; this last guideline is currently the most practical available and applies over a wide range of genetic models and correlation structures between markers.
