Calculation of percentage of cases on file with an unnamed father in 100 one-man and 100 two-man cases (filiation cases) from South-West Germany in 1976-1981. Ratio of defendants to witnesses among non-excluded men in two-man cases.

Applying the formula of Schulte-Mönting and Hummel to 100 one-man affairs (filiation cases) in South-West Germany between 1979 and 1981 gave a realistic prior probability of paternity of 0.837 +/- 0.0372. This means that in approximately 83.7% of all one-man affairs the man named by the mother to be the father of her child is indeed the father. For two-man affairs a realistic prior probability of paternity of 0.863 +/- 0.0369 was calculated on the basis of 100 two-man affairs in South-West Germany between 1976 and 1981. In other words, there is a probability of about 86.3% that a non-excludable man--irrespective of other factors--in a two-man affair is the real father of the child. In approximately 13.7% of two-man affairs neither the "defendant" nor the witness is the father, but a third unknown person. In about 85.7% of the two-man affairs in which a father of the child was named the "defendant" is in fact the father and in 14.3% the "witness" is the father.