Task 1: How to Select the Correct Weights for NHANES III Analysis

To select the correct weights for NHANES III data, you need to first check all variables in your analysis and select the weight of the smallest analysis subpopulation.  Separate weights are provided for those who completed the interview, MEC exam, MEC + home exam, or are part of one of 4 subsamples (AM exam subsample, PM exam subsample, allergy or central nervous system (CNS) exam subsample). See the Table below for the correct weights for each component.

Appropriate Uses of the NHANES III Sampling Weights

Examples

• Were all of the variables collected in the in-home interview? Click to see Example 1.

  Example 1

  You are performing an analysis to look at the association of race/ethnicity, and poverty on previous diagnosis of diabetes, using all 6 years of NHANES III data. All of these variables were collected in the in-home interview.

  ANSWER: You would use the interview weights for your analysis (wtpfqx6).

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• Were some of the variables collected in the MEC? Click to see Example 2.

  Example 2

  You are performing an analysis looking at the association of race/ethnicity, age, poverty and the prevalence of high blood pressure, using all 6 years of NHANES III data. All three demographic variables were collected during the in-home interview. For the blood pressure variables, you only want to include the average of the 3 measurements collected during the MEC exam. MEC-examined sample persons are a subset of those interviewed in the survey.

  ANSWER: You would use the MEC exam weight for your analysis (wtpfex6).

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• Were some of the variables collected in the MEC, plus the Home Exam? Click to see Example 3.

  Example 3

  You are performing an analysis looking at the association of race/ethnicity, age, poverty and the prevalence of high blood pressure, using all 6 years of NHANES III data. All three demographic variables were collected during the in-home interview. For the blood pressure variables, you want to include not only the measurements collected during the MEC exam, but also measurements collected during the Home Exam. MEC-examined sample persons are a subset of those interviewed in the survey. Home Examination was offered to those who could not attend the MEC exam.

  ANSWER: You would use the MEC+Home Exam weight for your analysis (wtpfhx6).

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• Were some of the variables part of a component subsample of the survey? Click to see Example 4.

  Example 4

  You are performing a logistic regression analysis looking at the association between fasting triglycerides and race/ethnicity, age, BMI and blood pressure on persons age 20 and over. Race/ethnicity and age were available from the in-home interview. Blood pressure and BMI came from the MEC exam. MEC-examined sample persons are a subset of those interviewed in the survey.  Fasting triglycerides are collected from those sample persons who were subsampled to do the 9 hour AM fast and who actually fasted. This group is approximately half the sample of those who were MEC examined.

  ANSWER: You would use the morning fasting subsample weights (wtpfsd6).

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