Key Concepts about the Physical Activity Monitor Data Files

Data from the physical activity monitor module are contained within the PAXRAW file, available on the Examination page of the NHANES website.  The PAXRAW file is a large data file (> 2 GB) and contains multiple records per participant. The file consists of sequential minute-by-minute records of activity intensity starting from the time the device began recording. For the 2003-2004 NHANES, a partial set of step count data may be accessible through the National Center for Health Statistics (NCHS) Research Data Center. The 2005-2006 survey cycle also includes data on number of steps.  Each participant in the PAXRAW file has up to 10,080 records, representing the number of minutes in the 7-day data collection (7 days*24 hours*60 minutes).

The intensity data are available in two formats: a DVD format (2 GB) and an online zipped file format. You will need to process the data to create summary variables for statistical analysis. SAS code has been provided by the National Cancer Institute (NCI) to facilitate the data processing.

NCHS and survey collaborators from the NCI performed initial data reviews on the data files to check for outliers and unreasonable values. The criteria used for reasonable ranges of activity count data were based on published literature and expert judgment. Notes pertaining to the variables in this file are provided in the data codebook.

Physical Activity Monitor

File Name: PAXRAW
Data Contained in the Data File:

• Component status code
• Device calibration code, indicating whether the accelerometer was within calibration tolerance upon return
• Observation day of the week
• Sequential observation number in minutes
• Hour and minute of observation
• Intensity value recorded by the accelerometer
• Step count recorded by the accelerometer (2005-2006 currently on public use files)