TY - JOUR
T1 - Nonrandom sampling in human genetics
T2 - Skewness and kurtosis
AU - Chakraborty, Ranajit
AU - Hanis, Craig L.
N1 - Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.
PY - 1987/1/1
Y1 - 1987/1/1
N2 - When a multivariate normal sample is chosen from a truncated space of one of its components one can no longer make use of the normality assumption for the sample observations or for the estimates derived from them. In this paper, skewness and kurtosis for each component are derived analytically under a broad class of nonrandom sampling. It is shown that the distortions in skewness and kurtosis produced by nonrandomness are negligible, except those for the component with respect to which the selection of sampling regions is based. The ususal tests of normality from sample values of skewness and kurtosis measures remain valid under nonrandom sampling, except for the selection variable. The implications of these analytical results in the context of commingling analysis in genetic epidemiology are discussed. It is recommended that when samples of families are obtained through nonrandomly ascertained probands, a commingling analysis should treat each relative class separately, since such analyses based on the pooled sample of individuals may involve unspecified bias in the levels of the test procedure.
AB - When a multivariate normal sample is chosen from a truncated space of one of its components one can no longer make use of the normality assumption for the sample observations or for the estimates derived from them. In this paper, skewness and kurtosis for each component are derived analytically under a broad class of nonrandom sampling. It is shown that the distortions in skewness and kurtosis produced by nonrandomness are negligible, except those for the component with respect to which the selection of sampling regions is based. The ususal tests of normality from sample values of skewness and kurtosis measures remain valid under nonrandom sampling, except for the selection variable. The implications of these analytical results in the context of commingling analysis in genetic epidemiology are discussed. It is recommended that when samples of families are obtained through nonrandomly ascertained probands, a commingling analysis should treat each relative class separately, since such analyses based on the pooled sample of individuals may involve unspecified bias in the levels of the test procedure.
KW - commingling analysis
KW - nonrandom samples
KW - tests of significance of normality
KW - truncated normal distribution
UR - http://www.scopus.com/inward/record.url?scp=0023179611&partnerID=8YFLogxK
U2 - 10.1002/gepi.1370040204
DO - 10.1002/gepi.1370040204
M3 - Article
C2 - 3582959
AN - SCOPUS:0023179611
VL - 4
SP - 87
EP - 101
JO - Genetic Epidemiology
JF - Genetic Epidemiology
SN - 0741-0395
IS - 2
ER -