Table 1

Distribution of vehicle year and confounding variables for cases and controls*

	Cases (n = 571)		Controls (n = 588)
	No	%	No	%
*Proportions of controls are adjusted for the cluster sampling design.
Vehicle year
<1984	118	23.9	58	8.9
1984–88	157	31.8	164	31.0
1989–93	169	34.2	207	37.8
⩾1994	50	10.1	133	22.4
Age group of driver (years)
<25	195	34.2	91	13.7
25–34	133	23.3	125	22.3
35–44	85	14.9	154	24.5
45–54	61	10.7	107	19.6
55–64	39	6.8	80	14.2
65+	58	10.2	31	5.6
Sex
Female	198	34.7	226	41.3
Male	373	65.3	362	58.7
Education level
Post-secondary	178	31.5	276	49.3
Secondary >3 years	137	24.2	154	25.1
<3 years secondary	252	44.4	157	25.6
Ethnicity
White/European	313	54.8	444	74.7
Maori	117	20.5	61	9.2
Pacific Islands	86	15.1	36	6.1
Other	55	9.6	47	10.0
Self reported alcohol (standard drinks in previous 6 hours)
0	418	76.4	537	95.4
1	15	2.7	15	1.8
2	20	3.7	21	2.7
⩾3	94	17.2	5	0.8
Marijuana use (last 3 hours)
No	520	94.2	582	99.5
Yes	32	5.8	5	0.5
Time of day
Not 2–5 am	525	91.9	571	99.6
2–5 am	46	8.1	17	0.4
Stanford sleepiness score
1–3 (not sleepy)	447	87.7	578	99.0
4–7 (sleepy)	63	12.3	8	1.0
Number of passengers
0	285	50.3	355	62.9
1	140	24.7	144	23.4
⩾2	142	25.0	88	13.7
Average driving (hours/week)
⩽5	219	42.1	171	30.5
6–10	205	39.4	216	39.3
11–20	63	12.1	135	22.3
21–30	11	2.1	32	3.8
>30	22	4.2	27	4.1
Type of licence
Never/disqualified	66	11.6	7	1.1
Learner/restricted	91	16.0	27	4.2
Full New Zealand car licence	402	70.8	546	93.1
Wearing seatbelt when crashed
No	81	14.7	16	1.8
Yes	469	85.3	568	98.2
Vehicle insurance status
Insured	322	56.5	514	88.3
Not insured	206	36.1	63	10.2
Don’t know	42	7.4	11	1.5
Self reported speed (kph)
0–30	87	16.9	78	13.9
31–50	113	21.9	229	41.5
51–80	196	38.1	220	33.7
>80	119	23.1	55	11.0
Current safety inspection certificate
Yes	466	81.6	559	95.5
No	105	18.4	29	4.5
Engine size (cc)
<2000	245	61.3	238	48.8
2000–2999	129	32.3	196	39.6
⩾3000	26	6.5	66	11.6