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Table 5 Description of the computation of the mobility indicators

From: Towards a comprehensive set of GPS-based indicators reflecting the multidimensional nature of daily mobility for applications in health and aging research

Mobility indicatorDay selectionDefinition of daily mobility indicator
MaxDistRLength of straight line connecting the home with the GPS fix furthest away from home
CHullRArea of convex hull enclosing all GPS fixes
SDEREllipse defined at one 1 SD containing approximately 68% of GPS fixes within the ellipse’s boundary
LengthPerTripMAverage length of a move
LocVarRCombined variance of X and Y coordinates [55]
DurPTMRTime spent in passive transport modes
TOHRDuration between all OH fixes, interpolating for up to 60-min gaps between consecutive GPS fixes if both fixes are OH
EntropyREntropy computed as in Saeb et al. [55]. Entropy measures how a participant’s time was distributed over the different stop locations: the higher the entropy, the more regularly time is distributed and/or the higher the number of unique locations
NumLocRNumber of OH locations visited
NumUniqLocMStops visited multiple times (referring to the same location cluster) during the included study days are only counted once
DurATMRTime spent in active transport modes
MaxDurATMRDuration of longest continuous trip using active transport modes
RevisitedLSMPercentage of the daily convex hull that has overlap with any convex hulls of the other included study days
AvgRevisitedLSMAverage percentage overlap of the daily convex hull with the convex hulls of the other included study days
SDDirMaxDistMDirection of most distant point from home. Weekly aggregation is done by circular SD: the larger the circular standard deviation, the more variability in day-to-day orientation of life space
GravCompactM\(K = P/(2\sqrt {\pi A} )\) (where P = perimeter of convex hull and A = area of convex hull. The higher the more elongated is the life space
Maj2MinAxisMRatio between major and minor axis of standard deviational ellipse
TimeMaxDistMTime of day starting at 3 AM [min] when most distant location from home is reached
TimeFirstMoveMTime of day starting at 3 AM [min] of the first move (approximation of first OH activity) of a day
TimePeriodActiveMAssignment of OH activities (moves and OH stops) based on start time to the classes morning (6 AM–12 noon), afternoon (12 noon–6 PM), or evening (6 PM–11 PM). A day is coded as 1 (morning day) if morning activities > evening activities; as 3 (evening day) if evening activities > morning activities; 2 (neutral timing day) in all other cases
  1. ‘Day selection’ refers to whether among the valid days a fixed number of days were selected completely at random (R) or only if days included at least one move (M). All daily indicators were summarized to weekly aggregates using the median, except for SDDirMaxDist, where the circular SD was used, and TimePeriodActive using the mean