Table 3.

Bland-Altman statistics^a.

Variable			PSGb-Fitbit		Lower LoAc		Upper LoA		P value
Sond (minutes)			–1.6		–68.8		65.6		.73
Soffe (minutes)			–5.6		–189.3		178.2		.66
TSTf (minutes)			–4.0		–204.3		196.3		.77
REMdg (minutes)			–2.7		–87.8		82.4		.67
lightdh (minutes)			–10.4		–136.8		116.0		.27
deepdi (minutes)			11.2		–72.9		95.2		.08
WASOj (minutes)			–37.1		188.1		113.8		.001
REMLk (minutes)			–29.4		–145.4		86.6		.001
HR10l (bpmm)
	Overall	0.9		–6.9		8.6		<.001
	WASO	1.9		–5.4		9.2		.03
	N1n	1.2		–8.9		11.3		.14
	N2o	0.6		–4.7		6.0		.001
	N3p	0.6		–6.4		7.6		.008
	REMq	0.7		–4.7		6.0		<.001

^aStatistics accompanying the Bland-Altman plots (Figure 5). Sleep onset and rapid eye movement (REM) sleep latency were calculated using the non–rapid eye movement (NREM) sleep stages 1 sleep onset criteria. The average 10%-trimmed heart rate and 10%-trimmed heart rate variance values in various sleep states are presented in the columns below the sleep variables. The average difference between polysomnography and Fitbit measures bias can be found in the first column. The lower and upper limits of agreement describe 1.96 times the SD around the bias and can be found in the subsequent columns. In the last column, the P values for the paired t test are reported; we tested whether the bias was significantly different from 0.

^bPSG: polysomnography.

^cLoA: limit of agreement.

^dS_on: sleep onset.

^eS_off: sleep offset.

^fTST: total sleep time.

^gREM_d: REM sleep duration.

^hlight_d: light sleep duration.

ⁱdeep_d: deep sleep duration.

^jWASO: wakefulness after sleep onset.

^kREML: REM sleep latency.

^lHR₁₀: 10%-trimmed heart rate average.

^mbpm: beats per minute.

ⁿN1: NREM stage 1 sleep.

^oN2: NREM stage 2 sleep.

^pN3: NREM stage 3 sleep.

^qREM: rapid eye movement.