Task 2: How to Identify Environmental Chemical Variable Names and File Locations

To identify the variables for your analysis, check the Laboratory Documentation for each two-year cycle.


Warning iconThe steps below assume that you have already familar with the data documentation available from the NHANES website. If you need instructions on how to access and download data documentation, please review the Locate Variables module in the Continuous NHANES Web Tutorial before continuing.



Beginning at the NHANES Homepage, click the NHANES 1999–2000 link under Questionnaires, Datasets, and Related Documentation; scroll down and click the Laboratory link in the Data, Documentation, Codebooks, SAS code section.

Phthlate Data (1999v2004)

On the Laboratory page, find the PHPYPA Urinary Phthalates in the 1999–2000 Laboratory Files section, click the Docs link under the heading PHPYPA Urinary Phthalates to review the survey Documentation, Codebook, and Frequencies, and then determine which ones might be applicable for your analysis.

Using the Back button to return to the NHANES Homepage, click the NHANES 2001–2002 link or the NHANES 2003–2004 link and repeat the steps above to review the corresponding survey Documentation, Codebook, and Frequencies. The 2003–2004 Laboratory File for urinary phthalates is named Lab 24 Urinary Phthalate, which is different from the previous two survey cycles.

Warning icon Urinary phthalate metabolites were measured in urine specimens of a one-third subsample of eligible participants ages six years and older in the MEC examination so the special subsample weights are required to analyze these data properly.

Urinary creatinine is usually used in analysis to adjust for urine dilution. URDMHPLC is used to identify the values that are below the limit of detection.


Laboratory Variables

Variable Name Variable Label Survey cycles
SEQN Respondent sequence number 99-00, 01-02, 03-04
WTSPH4YR Phthalate Subsample 4 Year Mec Weight 99-00, 01-02
WTSPH2YR Phthalate Subsample 2 Year Mec Weight 99-00, 01-02
WTSB2YR Two-year MEC weights of subsample B 03-04
URXMHP Mono-(2-ethyl)-hexyl phthalate (ng/mL) 99-00, 01-02, 03-04
URDMHPLC Mono-(2-ethyl)-hexyl phthalate comment 03-04
URXUCR Creatinine, urine (mg/dL) 99-00, 01-02, 03-04



The analysis of NHANES environmental chemical data should be conducted with the appropriate survey design, demographic variables and any other covariates that are applicable. Using the Back button to return the survey cycle of interest, click the demographics link and then click docs. The Adobe Acrobat PDF file of the survey Documentation, Codebook, and Frequencies for the demographics portion of the questionnaire will open. Review the Documentation and determine which variables are applicable to your analysis.

Demographic Variables

Variable Name Variable Label
SEQN Respondent sequence number
SDDSRVYR Data Release Number
RIDSTATR Interview/Examination Status
SDMVPSU Masked Variance Pseudo-PSU
SDMVSTRA Masked Variance Pseudo-Stratum
RIDAGEYR Age at Screening Adjudicated Recode
RIAGENDR Gender Adjudicated
RIDRETH1 Race/Ethnicity Recode




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