To find the genetic factors involved in a particular disease, one can proceed as follows. First a certain region of interest in the genome is identified, possibly from earlier inheritance studies. In this region one locates a set of tag SNPs from the HapMap data; these are SNPs that are very well correlated with all the other SNPs in the region. Thus, learning the alleles of the tag SNPs in an individual will determine the individual's haplotype with high probability. Next, one determines the genotype for these tag SNPs in several individuals, some with the disease and some without. By comparing the two groups, one determines the likely locations and haplotypes that are involved in the disease.