Key Concepts About Identifying Correct Sample Weights and File Locations

Most of the environmental chemicals were measured in randomly selected subsamples of examined person within specific age groups. Subsample weights were constructed for each two-year survey cycle to account for the complex survey design (including oversampling), survey non-response, and post-stratification.

Warning icon When analyzing environmental chemical data, it is important to select the correct subsample weight variable.

Several subsample weights are associated with the NHANES environmental chemical data, and different environmental chemicals measurements may have accompanying subsample weights or share the same subsample weights depending on the chemical group of interest. Generally, when environmental chemicals were measured in randomly selected subsample of the survey participants, the data files contain specific subsample weight variables. The 1999–2000 and 2001–2002 data files and documentation includes two-year and four-year subsample weights. The four-year weights are used when the 2001-2002 data are combined with 1999–2000 data to produce a combined estimate for 1999–2002.

The following is an information note from the Continuous NHANES Web Tutorial:

Continuous NHANES Web Tutorial - Weighting module

 

Info icon Beginning in 2003, the survey content for each two-year period is held as constant as possible to be consistent with the data release cycle. In the first four years of the continuous survey (1999–2002), this was not always the case, and special data release and access procedures had to be developed for selected survey content collected in "other than two-year" intervals. (For more details see the NHANES Data Release and Access Policy [PDF - 48 KB] ).

 

Variables for Subsample Weights

Chemical Group Specimens 1999-2000 Subsample Weight Variable Names 2001-2002 Subsample Weight Variable Names 2003-2004 Subsample Weight Variable Names
Metals        
Heavy Metals Urine WTSHM2YR, WTSHM4YR WTSHM2YR, WTSHM4YR WTSA2YR
Total Arsenic and Speciated Arsenics

Urine

na na WTSA2YR
Persistent organic pollutants        
 Dioxins, Furans, and Coplanar Polychlorinated Biphenyls (PCBs) Serum WTSPO2YR, WTSPO4YR WTSPO2YR, WTSPO4YR WTSC2YR
 Non-dioxin-like Polychlorinated Biphenyls (PCBs) Serum WTSPO2YR, WTSPO4YR WTSPO2YR, WTSPO4YR WTSC2YR
  Organochlorine Pesticides Serum WTSPO2YR, WTSPO4YR WTSPO2YR, WTSPO4YR WTSB2YR
Polybrominated Diphenyl Ethers and Polybrominated Biphenyl Serum na na WTSB2YR

Polyfluoroalkyl Compounds

Serum

na na WTSA2YR

Polycyclic Aromatic Hydrocarbons

Urine

WTSPH2YR, WTSPH4YR WTSPH2YR, WTSPH4YR WTSB2YR

Phthalates

Urine

WTSPH2YR, WTSPH4YR WTSPH2YR, WTSPH4YR WTSB2YR

Phytoestrogens

Urine

WTSPH2YR, WTSPH4YR WTSPH2YR, WTSPH4YR WTSB2YR

Pesticides

Urine

WTSPP2YR, WTSPP4YR WTSPP2YR, WTSPP4YR WTSC2YR

Environmental Phenols

Urine

na na WTSC2YR

Perchlorate

Urine

na na WTSC2YR

Volatile Organic Compounds

Whole Blood 

WTSVOC2Y, WTSVOC4Y WTSVOC2Y WTSVOC4Y WTSVOC2Y

 

 

 

 

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