TABLE 1.

Median Incidence Rates and Rate Ratios for Crashes and Near Crashes per 10 000 Miles and G-Force Events per 100 Miles Among Newly Licensed Adolescent Drivers and Their Parents, Blacksburg and Roanoke, VA, June 2006–September 2008

Event	Overalla	Quarter 1	Quarter 2	Quarter 3	Quarter 4	Quarter 5	Quarter 6	Pb
Crashes and near crashes
Adolescents, IR	7.43	9.15	11.68	7.48	5.29	3.90	7.09	.019
Parents, IR	1.90	1.25	2.94	3.55	1.39	0.94	0.98	.168
IRR	3.91	7.32	3.98	2.11	3.80	4.13	7.21	.422
G-force events
Rapid starts
Adolescents, IR	1.02	1.33	1.20	0.87	0.80	0.85	0.80	.034
Parents, IR	0.23	0.33	0.27	0.16	0.20	0.17	0.10	.005
IRR	4.35	3.98	4.47	5.53	4.08	4.92	8.05	.435
Hard stops
Adolescents, IR	0.91	1.14	1.20	0.96	0.90	0.96	1.01	.122
Parents, IR	0.20	0.24	0.16	0.23	0.19	0.15	0.19	.220
IRR	4.58	4.73	7.39	4.09	4.68	6.64	5.46	.144
Hard left turns
Adolescents, IR	0.70	0.62	0.63	0.72	0.79	0.80	0.82	.931
Parents, IR	0.02	0.02	0.02	0.03	0.03	0.02	0.02	.974
IRR	29.02	29.77	28.00	24.21	27.12	33.93	35.51	.988
Hard right turns
Adolescents, IR	0.31	0.23	0.29	0.41	0.39	0.33	0.50	.022
Parents, IR	0.01	0.01	0.01	0.02	0.02	0.02	0.01	.270
IRR	23.29	18.75	35.42	17.61	21.08	21.98	76.08	.283
Yaw
Adolescents, IR	0.14	0.15	0.13	0.16	0.13	0.14	0.15	.888
Parents, IR	0.04	0.05	0.05	0.03	0.03	0.03	0.03	.609
IRR	3.50	2.86	2.71	5.24	4.48	4.65	4.34	.679
Composite
Adolescents, IR	4.16	4.52	4.65	4.37	3.87	4.44	4.79	.510
Parents, IR	0.82	0.93	0.82	0.83	0.75	0.67	0.61	.484
IRR	5.08	4.84	5.66	5.29	5.15	6.57	7.85	.455

Note. IR = incidence rate; IRR = incidence rate ratio. Adolescents had 37 crashes and 242 near crashes, and their parents had 2 crashes and 32 near crashes during the study period.

^aOverall IRR for crashes and near crashes and overall and quarterly IRRs for g-force events were statistically significant from 1 (P < .001).

^bDerived from likelihood ratio test that an IR or IRR was constant over time; individual IRR's were different from 1 (P < .001).