Exploring Family Relations between International Patent Applications

In the international system for granting patents for inventions, first patent filings can be followed by subsequent filings at other patent offices within one year. Each such group of related filings constitutes a patent family. Tests are developed as to whether the observed number of first filings that leads to subsequent filings (r) is in agreement with a random process of assignment of the hits from the subsequent filings. An exact expression for the random distribution can be used for small sized data sets. Its behaviour and also the behaviour of an asymptotic Poisson approximation as well as a censored binomial distribution for r are assessed. The approach is stimulated by the Fisher-Wright model in population genetics and possible parallel applications to other biological processes are sought, such as transformations of stem cells and cancer.