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

To select the correct weights for NHANES II 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 have completed the interview, MEC exam, or are part of one of the six subsamples. See the Table below for the correct weights for each component or subsample.

Appropriate Uses of the NHANES II 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 with previous diagnosis of diabetes. All of these variables were collected in the in-home interview.

  ANSWER: You would use the medical history interview final weight for your analysis (N2AH0288).

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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. 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 two seated 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 examined weight for your analysis (N2AH0282).

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• Were some of the variables part of a component subsample of the survey? Click to see Example 3.

Example 3

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. Triglycerides were measured from those sample persons who were subsampled to do the oral glucose tolerance test and were instructed to fast for from 10-16 hours. This group is approximately half the sample of those who were MEC examined.

ANSWER: You would use the oral glucose tolerance test final examined weight (N2AH0294).

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It is important to check all the variables in your analysis and use the weight of the smallest sample subpopulation. Otherwise you will not obtain estimates appropriately adjusted for survey non-response.

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