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NHANES Physical Activity and Cardiovascular Fitness Data Tutorial

Preparing a Cardiovascular Fitness Dataset

Purpose

Module 6 illustrates the basic principles for preparing a cardiovascular fitness dataset. We encourage you to approach the following tasks in sequence so that you replicate the steps you will need to take when you conduct an analysis of NHANES data. To help guide you through this process, we’ve created a SAS program titled “CVXMSTR.SAS” that demonstrates how to prepare a cardiovascular fitness analytic dataset. We’ll use this program to assess estimated maximal oxygen uptake (VO2 max) among NHANES study participants.

 

Task 1: Locate Variables

Cardiovascular fitness data files and supporting documentation are stored in the Examination section of the NHANES website.  This task will teach you how to identify cardiovascular fitness variables, appropriate sample weights, and their file locations.

Identify Cardiovascular Fitness Variables and File Locations

Identify Correct Sampling Weights and File Locations

Task 2: Download Data

To organize your data most effectively, it is helpful to create folders in which to save your data files, documentation, and extracted SAS datasets. 

Create a Directory

Download Data Files and Supporting Documentation

Extract and Save Data Files

Task 3: Merge & Append Datasets

Typically, an NHANES cardiovascular fitness analytic dataset will include data collected during two or more cycles. You will need to merge the data to include variables from both demographic data files and cardiovascular fitness examination files collected within the same cycle and append the data to combine years of data from multiple cycles.

Task 4: Review Data & Create New Variables

Before you can use the variables in the cardiovascular fitness dataset, you will need to review the data and may need to create new variables.  For example, you may need to adjust the NHANES data if the dataset has missing data or outliers.  You also may need to create new variables, including reconstructed weight variables when combing data from multiple NHANES cycles.

Evaluate Missing Data

Estimate VO2 Max

Check Distributions and Describe the Impact of Influential Outliers

Task 5: Format & Label Variables

Formats and labels are user-defined tools that provide a convenient way to describe variables in your SAS output.  Although adding formats or labels to your variables is optional, it is often helpful when reviewing the output from your analyses. 

Task 6: Save a Dataset

In this module, you will learn how to create a permanent dataset in a SAS library.  This will allow you to save the temporary dataset that you have been working with as a permanent file on your computer so you can continue your work at a later time.

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