Table 1.
Comparison of ISCOLE and 2003–2006 NHANES on accelerometer data collection and data management factors
| 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 |
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.
Details for NHANES data management located at http://www.cdc.gov/nchs/nhanes/nhanes2003-2004/PAXRAW_C.htm.