A NEW APPROACH TO DESIGN AND DATA ANALYSIS
FOR CPP-BASED STUDIES THAT MAKE USE OF SERA, AND EXPERIENCE
WITH RECENT LABORATORY ANALYSIS OF CCP SERA
Matthew P.
Longnecker*, John Brock, Haibo Zhou, Mark Klebanoff.
Epidemiology Branch, National Institute of Environmental
Health Sciences, NIH National Center for Environmental
Health, CDC, Department of Biostatistics, University of North
Carolina, Chapel Hill, National Institute of Child Health and
Human Development
Using the Collaborative
Perinatal Project (CPP) data set and serum repository, the
authors are testing a number of hypotheses about health
effects of in utero exposure to background levels of
persistent environmental contaminants. For example, maternal
serum level of polychlorinated biphenyls is being used to
estimate in utero exposure to these suspected
neurotoxins. Outcomes of interest are findings on neonatal
neurologic exam, Bayley Scale of Infant Development, and WISC
IQ.
In addition to making use of
the relatively new case-base study design, we are also
developing statistical methods that allow us to use an
efficient sampling scheme for continuous outcomes. For
example, in studying IQ as an outcome, besides analyzing
blood from a random sample of the cohort, we are also
analyzing specimens from a random sample of subjects whose IQ
is either above or below one standard deviation of average.
For a given total number of specimens analyzed this
“oversampling” of subjects in the tails of the
outcome distribution increases our power to detect
associations relative to simple random sampling alone. The
gain in statistical efficiency is marked when the relation
under study is not completely linear. A proper statistical
method for analyzing data sampled in this manner is being
developed and will be discussed; ignoring this type of
sampling in the analysis will cause bias in parameter
estimation.
To work with these older
serum specimens, we have had to modify the laboratory
analytical techniques to work around the frequent finding of
precipitates in the stored specimens. In addition, we will
report the findings from analysis of the specimens for
sodium, which reflects the amount of desiccation.