This file includes the genetic relatedness coefficient for all pairs of individuals with
genomic data. The relatedness measure is based on a calculated coefficient of relatedness
that summarizes the correlation in genomic data for all participant pairs.
The genetic relatedness measure can be used to characterize the biological relatedness among
pairs of observations, with, for example, a value of 1.0 for identical twins, 0.5 between a
parent and child and between full siblings, and 0.25 between half-siblings. The relatedness
measure was derived through the identity-by-descent function within the PLINK software Version 1.9
(see https://www.cog-genomics.org/plink/1.9/ibd).
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The relatedness file includes an additional set of variables, which is two pairs of
identification variables to allow the data to be merged with other data from CDS-2014
or from Core PSID (or other PSID supplements). These identification variables are available
for both individuals for whom the corresponding relatedness coefficient is calculated.
The relatedness file includes a total of 3,156,328 observations, which corresponds to the
lower diagonal elements of the symmetric relatedness matrix. The count is obtained as the
squared number of cases minus the number of cases divided by two:
(2,513² – 2,513) / 2 = 3,156,328.
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