Table 3.

Chest compression variability

	Baseline unaided					Smartwatch-based feedback device
	N	Mean	Median	SD	CV	N	Mean	Median	SD	CV
Depths
All	8121	2.19	2.26	0.60	26.6%	7896	2.05	2.06	0.31	14.9%†
IH rescuers	2913	2.10	2.15	0.43	20.3%	2836	2.05	2.06	0.17	8.5%†
OH rescuers	2870	2.50	2.49	0.41	16.3%	2792	2.09	2.08	0.26	12.6%†
Lay rescuers	2338	1.91	1.77	0.78	41.1%	2268	1.99	2.03	0.44	22.3%†
Rates
All	8121	125	123	21	16.9%	7896	115	114	7	6.3%†
IH rescuers	2913	134	134	18	13.8%	2836	114	113	4	3.5%†
OH rescuers	2870	121	119	9	7.2%	2792	114	114	7	5.8%†
Lay rescuers	2338	119	123	29	24.0%	2268	117	115	10	8.5%†

Data are reported as mean ± SD. N represents number of compressions analyzed.

CV = coefficient of variation; IH = in-hospital; OH = out-of-hospital.

^†P < .001 between unaided and smartwatch-based feedback device for all parameters compared.