Table I.

Descriptive Statistics, Significance Levels, and Effects Sizes for the Direct Test of Intervention Effects

	Pre-test						Post-test
	Treatment (n = 107)			Control (n = 99)			Treatment (n = 107)			Control (n = 99)			Condition × Time
Outcome measure	M	SD	R	M	SD	R	M	SD	R	M	SD	R	F	p	η2
Observational bike helmet score	2.2	0.8	0–3	2.1	0.7	0–3	2.4	0.7	1–3	2.0	0.7	0–3	7.28	.008	.03
Computerized measures
Helmet skill discrimination	0.5	0.6	0–2	0.5	0.6	0–2	1.8	0.4	0–2	0.5	0.6	0–2	230.31	<.001	.53
Safety rules	2.7	0.7	0–4	2.7	0.7	0–4	3.7	0.7	1–4	2.7	0.7	0–4	67.46	<.001	.25
Hazard discrimination	9.9	2.3	3–13	10.0	2.4	4–14	14.6	1.2	6–17	11.1	2.2	4–14	104.96	<.001	.34

Note. M: mean; SD: standard deviation; R: range; for η² a value of .10 is a small effect, .30 is a medium effect and .50 is a large effect.