Quantification of Outdoor Mobility by Use of Accelerometer-Measured Physical Behaviour

Table 2

(a) Group differences in physical behavior. (b) Results of receiver operating characteristic curve between measures of physical behaviour and reports on outdoor mobility ().

(a)

	“Not outdoors” versus “outdoors”					“Not outdoors alone” versus “outdoors alone”
	Group 0, Figure 1		Groups 1, 2, and 3, Figure 1		Independent	Groups 0 and 1, Figure 1		Groups 2 and 3, Figure 1		Independent
	()		()		-test	()		()		-test
	Mean	(SD)	Mean	(SD)		Mean	(SD)	Mean	(SD)
Mean upright time per day (min)	114.8	(100.3)	265.2	(119.4)	<0.001	127.9	(104.1)	291.7	(107.2)	<0.001
Mean number of upright events per day	35.0	(21.9)	48.2	(17.3)	<0.001	36.2	(21.3)	50.4	(15.9)	<0.001
Mean length of upright events (min)	2.9	(1.5)	5.8	(2.8)	<0.001	3.3	(1.9)	6.2	(2.7)	<0.001
Maximum length of upright events (min)	21.7	(14.7)	62.3	(34.7)	<0.001	26.3	(23.7)	68.5	(31.8)	<0.001
Median length of upright events (min)	1.8	(0.9)	2.7	(1.3)	<0.001	2.0	(1.1)	2.8	(1.3)	<0.001
Upright event variability (min)	2.8	(1.7)	5.8	(3.5)	<0.001	3.2	(2.2)	6.3	(3.5)	<0.001

The NADL question used was if the participants had been walking outdoors the past 14 days. “Not outdoors”: participants who had not walked outdoors; “outdoors”: participants who had walked outdoors either alone, alone with difficulty, or with assistance; “not outdoors alone”: participants who had not walked outdoors or walked outdoors with assistance; “outdoors alone”: participants who reported walking outdoors alone or alone with difficulty. Mean upright time per day (min): total minutes of all upright events/number of recording days; mean number of upright events per day: average number of upright events per day; mean length of upright events: average length in minutes based on all upright events during the recording period; maximum length of upright events: maximum length in minutes for the longest upright event during the recording period; median length of upright events: median length in minutes based on all upright events during the recording period; upright event variability: the interquartile range (IQR) of upright events lengths in minutes during the recording period.

(b)

Measure of PB	Outdoor mobility					Independent outdoor mobility
	AUC	95% CI	SENS	SPEC	CP	AUC	95% CI	SENS	SPEC	CP
Mean upright time per day	0.836	0.78–0.89	0.805	0.716	157.7	0.865	0.82–0.91	0.802	0.754	198.9
Mean number of upright events per day	0.697	0.62–0.77	0.805	0.531	34.8	0.707	0.64–0.77	0.802	0.526	36.8
Mean length of upright events	0.834	0.78–0.89	0.811	0.679	3.4	0.838	0.79–0.89	0.802	0.719	4.0
Maximum length of upright events	0.871	0.83–0.91	0.805	0.704	30.8	0.891	0.85–0.93	0.802	0.833	41.2
Median length of upright events	0.732	0.66–0.80	0.805	0.519	1.7	0.719	0.66–0.78	0.802	0.535	1.8
Upright event variability	0.804	0.75–0.86	0.805	0.605	3.2	0.810	0.76–0.86	0.802	0.640	3.5

AUC: area under receiver operating characteristic curve; CP: cut-off point for predictors above which subject is more likely to report that they are outdoor walking; : sample; SENS: sensitivity; SPEC: specificity; PB: physical behaviour; mean upright time per day: total minutes of all upright events/number of recording days; mean number of upright events per day: average number of upright events per day; mean length of upright events: average length in minutes based on all upright events during the recording period; maximum length of upright events: maximum length in minutes for the longest upright event during the recording period; median length of upright events: median length in minutes based on all upright events during the recording period; upright event variability: the interquartile range (IQR) of upright events lengths in minutes during the recording period.