The Logarithm of Odds (LOD) score method for testing linkage was first proposed by Dr Newton Eniss Morton in 1955 although the underlying principles were previously set out by Professor Cedric Austen Bardell Smith. It is a statistical measure of the likelihood that two genetic markers occur together on the same chromosome and are inherited as a single unit of DNA. The calculation of LODs requires generational pedigree analysis, with higher LODs reflecting greater probability of linkage. A score of greater than 3 is generally taken as evidence for linkage.
In 1955 Renwick and Dr Sylvia Dorothy Lawler published a series of family trees demonstrating linkage between the ABO blood groups and the Nail-Patella Syndrome. The first calculations had to be done by hand. Renwick was a pioneer in devising computer programs for calculating LODs. In 1961 he and Dr Jane Schulze wrote a computer program for detailed analysis of pedigrees and calculation of points on a likelihood ratio curve.