Table of Contents

Component Description

In NHANES 2007-2008, a weighted pooled-sample design was implemented to facilitate pooling samples before making analytical measurements for specific environmental chemicals. Pooling samples allows for larger sample volumes, which can result in lower limits of detection and reduces the number of measurements and costs. Laboratory components analyzed with the pooled-sample design in the NHANES 2007-2008 cycle includes:

The analytic pools were prepared from serum collected from a random one-third subset of the NHANES 200-2008 participants aged 12 years and older. Samples were pooled based on gender, race and Hispanic origin, and age. This Pooled-Sample Technical Support file (POOLTF_E) contains information on individual participants included in each pool. Three variables are included in the technical support file:

SEQN - Respondent sequence number, the unique survey participant identifier that can be used to link to the other NHANES data files;

SAMPLEID - Pool identification number, indicating which pool the participant was designated to; this is the key variable corresponding to the pooled-sample laboratory component datasets;

WTSA2YRA - The adjusted subsample weight for the individual survey participant.

If a survey participant was selected as part of the one-third subsample but did not provide a serum specimen or a specimen with sufficient volume for the analyses, he/she would not be assigned to a pool. The survey participant will be coded with “SAMPLEID=.” and “WTSA2YRA=0”.  In NHANES 2007-2008, there are 2282 individuals selected into the one-third subsample, and among them, 2070 provided sufficient volume of analytic specimen. Their specimens were used to create 260 pools with 2-8 samples per pool.

Please refer to the documentations accompanying each laboratory components using the pooled-sample design for more details on rationale and methods used to create pooled results.