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NHANES Physical Activity and Cardiovascular Fitness Data Tutorial

Preparing a Physical Activity Monitor Dataset

Purpose

Module 7 illustrates the basic principles for preparing a physical activity monitor dataset.  We encourage you to approach the following tasks in sequence so that you replicate the steps taken by an NHANES analyst.  To help guide you through this process, we’ve created a SAS program entitled “PAXMSTR.SAS” that demonstrates how to use the physical activity monitor data to calculate mean total counts per day, mean counts/min per day, and time above specified intensity thresholds for study participants. Investigators interested in physical activity monitor data commonly analyze these metrics.  Our dataset will contain these calculated metrics for each NHANES 2003-2004 and 2005-2006 participant with the necessary accelerometer data for the calculations.

When you have completed the tutorial and want to prepare a dataset for your own analysis, you may choose to perform an analysis that summarizes the physical activity monitor data in a different way.  You can still use this SAS program and tutorial as a framework for preparing your dataset and building your own analysis.

Info iconIMPORTANT NOTE

The SAS codes and data files are applicable to the 2003-2006 NHANES data only. These SAS codes will not work for 2011-2014 physical activity monitor data due to significant changes in data collection.

Task 1: Locate Variables

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

Identify Physical Activity Monitor 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 physical activity monitor 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 physical activity monitor 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 physical activity monitor dataset, you will need to review the data and create new variables.    

Evaluate Missing Data

Create New Variables

Create Summary Metrics

Check Distributions and Describe the Impact of Influential Outliers

Task 5: 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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