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89 Z. Rechtsmedizin 1 (1982-1983)

handle is hein.journals/injlegame89 and id is 1 raw text is: Zeitschrift fur
Z Rechtsmed (1982) 89:1-20                            Rechtsmedizin
© Springer-Verlag 1982
Originalarbeiten / Original Works
Mathematical Aspects of the
Paternity Index I = X/Y, Especially in Relation
to the Chance of Non-exclusion of Non-fathers*
L. E. Nijenhuis
Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam,
The Netherlands
Summary. In a previous paper the author mentioned some aspects of the
paternity index I (=X/Y): Among false triplets the frequency of those with I
equal to or higher than an (observed) I value of I is considerably lower than
1/IX; among false triplets the mean value of I is equal to 1, and among non-
excluded non-fathers it is equal to the inverse of the chance of non-exclusion;
among true triplets the mean value of 1/I (= i) is equal to the chance of non-
exclusion of non-fathers. In a statistical material rather strong deviations from
some of these expectations were observed.
In the present paper further characteristics of the distribution of I values
were taken into consideration, and especially those that should hold if lnI
would fit in with a normal distribution. It was supposed that with the aid of
such a distribution the deviations mentioned above could be recognized as
chance variability. It appears, however, that neither the logarithms of the
paternity index, nor those of the zygosity index of twins (chosen as an
analogous model that is more easily analysable than the paternity index) are
really normally distributed. This, in turn, makes that estimates of probability of
paternity, based on such a supposition, are of doubtful reliability. Besides it is
concluded that also for other reasons other estimates than Essen-Moller's
W (or I or i), as probability of first type errors, lead in practice to conclusions
that are equally subdue to a priori suppositions as are W values and may be, in
fact, much more erroneous than those.
Special attention is paid to the statistical analysis of paternity studies with
more than one alleged father, and it is concluded that in such cases the general
formula that may be considered to be equivalent with Essen-Moller's formula
for one-man paternity cases, i.e., W=X/(X+ Y) or I/(I+ 1), must be W =
I/(I+n); W=12/(I+n) etc. and certainly not W=I1/.(XI+1); W2=lz2/
(XI+ 1) etc.
Key words: Paternity index, paternity cases - Blood group expertise, paternity
index
* Dedicated to Prof. Dr. Erik Essen-M6ller on the occasion of his 80th birthday

0044-3433/82/0089/0001/$ 4.00

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