Cystic fibrosis is a hereditary disease that affects the mucus glands of the lungs, liver, pancreas, and intestines, causing progressive disability due to multisystem failure. The CFTR gene, found in Chromosome 7, is the cause of cystic fibrosis, where mutations result in proteins that are too short because of premature end to production. We have been analyzing **data** on cystic fibrosis for the School of Medicine, Medical College of Georgia, and because of confidentiality issues we cannot present these **data** in this paper. Although these **data** are very sparse with only a few individuals reported cystic fibrosis in southern Georgia, our **data** set has the same structure as one that has been used repeatedly in the literature. Table 1 gives a set of **data** on cystic fibrosis, which was presented by Crow [3] to illustrate the need to take account of the method of ascertainment in segregation analysis. One can countthe total number of offspring to be 269, the total number of affected offspring to be 124, and the total number of probands to be 90. Thus, one might estimate the segregation ratio to be 124/269 = .4610, and the ascertainment probability to be 90/124 = .7258. Again, these simple estimates are too inflated. Note that 46.1% is far in excess of the 25% expected on simple recessive inheritance (cystic fibrosis is autosomal recessive). One reason for the excess is the ascertainment bias -the exclusion of families where the parents are heterozygous, but fail to have a homozygous recessive child. These would add to the number of normal children and thereby reduce the proportion affected. This **data** set was also used in [4] for illustration.