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Table 1 Comparison of ISCOLE and 2003–2006 NHANES on accelerometer data collection and data management factors

From: Improving wear time compliance with a 24-hour waist-worn accelerometer protocol in the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE)

 

ISCOLE (2012–2013)

NHANES 2003-2006

Data collection

 Instrument

Actigraph GT3X+

Actigraph 7164

 Instrument initialization

Started data collection at midnight of the day the device was received, data collected at 80 Hz.

Started data collection when device was received, data collected at 60 sec epochs.

 Instrument wear regimen

Worn at mid-axillary line, lying on the iliac crest for 24 hours, removing while bathing and swimming (even though GT3X+ is a waterproof device).

Worn at mid-axillary line, lying on the iliac crest during wake time, removing while bathing and swimming.

 Instrument wear instructions

Instructions were read and a hard-copy paper was handed out.

Instructions were read and a hard-copy paper was handed out.

 Compliance enhancing strategies

In U.S. ISCOLE: Phone calls, daily visits to school, small daily incentives (e.g., erasers, stickers).

Monetary incentive, available by phone to answer questions or concerns, reminder postcard for return mailing of instrument.

 Instrument return

Research staff collected the devices from the children.

Instruments were mailed back to NHANES warehouse.

 Data download

Raw data downloaded and processed simultaneously. Processed data were in 1 sec epoch with the low frequency filter and included the 3 axis of orientation, steps, lux, and inclinometer.

Processed data in 60 sec epochs contained activity counts in the x-axis and steps.

 Immediate determination of valid data

Using a simple algorithm, data checked to include ≥ 4 days, including 1 weekend day with > 10 h/day of wear time

Only checked whether downloaded or not downloaded

 Participant checklist

Used to track instruments’ serial numbers, distribution and return dates, as well as record compliance checks.

Computerized management system

 Data transfer

Data were uploaded to a secure website to be retrieved by the coordinating center

Not necessary

Data management

 Visual quality control check

File names and file sizes were checked

Screened for possible outliers and code data as reliable or questionable

 SAS dataset creation

Files were re-integrated to 60 sec epochs and combined into a country specific dataset

Details not available

 Automated quality control checks

Using an automated process, instrument serial number, distribution and return dates were checked against the participant checklist

Details not available

 Final dataset

Once data checks were completed 3 datasets were created, 60 sec epoch with low frequency extension, 60 sec epoch with regular filter, and 15 sec epoch with low frequency extension.

Details not available

 Data organization

Date, time, sequence of data and day of the week variables were created.

Date, time, sequence of data and day of the week variables were created.

Additional variables (e.g., vector magnitude) were created and processes (e.g., separating date and time) were undertaken

 Initialization errors

Verified devices were initialized midnight of the first day

Details not available

 Additional cleaning

The last day of data was deleted as well as any day after 7 days of data collection

Details not available

 Finalization

Once all queries were resolved sequential 24-hour days were identified and labeled for midnight-to-midnight and noon-to-noon analysis

Details not available

  1. N.B. Details for ISCOLE data collection and data management presented in Additional file 1. Details for NHANES data collections located at http://www.cdc.gov/nchs/data/nhanes/nhanes_05_06/BM.pdf.
  2. Details for NHANES data management located at http://www.cdc.gov/nchs/nhanes/nhanes2003-2004/PAXRAW_C.htm.