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Troiano (2007) Wear Time Validation Parameters

Last Updated: Feb 21, 2018 02:51PM CST
The Wear Time Validation (WTV) tool in ActiLife allows users to easily flag invalid data (or, data collected when a device was not worn) for exclusion from further analysis.  WTV also provides a summary of the wear-time and non-wear time results from the datasets.  The Data Screening Criteria allow users to define non-wear periods.  Data flagged as non-wear is not removed from the *.agd file - it is simply flagged  as "wear time" or "non-wear time".
 
The Troiano technique was derived from the original SAS code that was developed to detect non-wear periods in the 2003-2004 NHANES dataset.  The original source code can be found at http://riskfactor.cancer.gov/tools/nhanes_pam/.  The parameters used by the algorithm can be customized in ActiLife to obtain a specific desired behavior.  Those parameters are defined below.
 
Define a non-wear period
This section provides options for defining the non-wear period.  ActiLife will use this information to scan the data for non-wear bouts.
  • Minimum Length (minutes or epochs) - This option sets the minimum required number or consecutive zeros (or data below the Activity Threshold if that feature is enabled) that must be encountered before a period is considered a "non-wear period."  After scanning the data and detecting the selected number of consecutive zeros, ActiLife will begin flagging data as "non-wear time."  The leading zeros detected during this process will be flagged retroactively (after they have been initially scanned).  Data will be flagged as "non-wear time" until the Spike Tolerance is exceeded.  That is, until the non-wear bout is broken by activity that exceeds 0 (or the Activity Threshold) for the number of times defined by Spike Tolerance.
  • Use Vector Magnitude - When checked, ActiLife scans the vector magnitude of three-axis data (when available) to detect wear or non-wear time.  When unchecked, ActiLife scans only Axis 1 (the vertical axis - see users' manual for details) to detect wear/non-wear times.  
  • Activity Threshold (per minute or per epoch) - This value represents the non-wear "floor."  When this feature is disabled, a non-wear bout is identified as periods of zeros (0s) in the data.  When enabled, any epoch below the set value will be considered as "zero."  Any epoch level over this threshold is considered a Spike
  • Max count level (per epoch or per minute) - Setting this option will flag epoch (or minute) counts that exceed this threshold as "zeros".  This option is useful if the dataset contains some corrupt data, for example, with large count levels.  This option does not mark the epochs directly as non-wear.
  • Spike Tolerance (number of minutes or epochs) - ActiLife will continue scoring a non-wear bout as non-wear until it detects more than the Spike Tolerance number of epochs above zero (or above the Activity Threshold, if that option is enabled).
  • Spike level to stop (count level per epoch or per minute) - If this option is set, a non-wear bout will end if a count level that exceeds this value is encountered.  This option allows the Wear Time Validation tool to mimic exactly the behavior of the 2003-2004 NHANES SAS code which eliminates non-wear time using the same technique.
  • Require consecutive epochs outside the activity threshold - To stop a non-wear period, you must have consecutive epochs with values above the Activity Threshold and exceeds the Spike Tolerance in time.
Optional Screening Parameters
  • Ignore wear periods less than _____ (minutes or epochs) - Because of the WTV algorithms used, some wear periods may be very short (shorter than the spike tolerance).  Use this option to set the minimum length of an acceptable wear period.
  • Minimum wear time per day (minutes or epochs) - Use this setting to flag an entire 24 hour day as invalid if there are less than the selected amount of valid (wear-time) minutes or epochs in the day.  
  • Minimum days of valid wear time - Use this option to flag an entire dataset as invalid if there are less than the minimum number of valid days.
  • Mark Sleep Periods as Wear Time - Use this option to flag pre-entered Sleep Periods as Wear-Time, regardless of activity levels.

Please refer to the following screenshot for the default settings for the Wear Time Validation Tool. If you are experiencing issues with Wear Time appearing to be either too high or too low, it is suggested that you reset these to the defaults and then adjust them to suit your needs:

wtv-defaults.png

 

If you need any further assistance, please visit our support portal at https://help.theactigraph.com/home. From there, you can view many helpful FAQ's and Troubleshooting Articles; log in to check any existing Support Requests; or create a new Support Ticket if you are unable to find a solution. You can also email us at support@theactigraph.com or give us a call at (877) 497-6996, Monday through Friday, 8 am to 5 pm CST.

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