	After PSM
	Exposed n=215		Unexposed n=95		p Value
	Mean	SD	Mean	SD	α
Behaviour	3.44	0.90	3.49	0.84	0.61
Intention to wear a helmet	6.04	1.70	6.17	1.32	0.44
Planning	3.11	0.88	3.02	0.86	0.42
Action self-efficacy	3.54	0.78	3.55	0.80	0.97
Outcome expectancies	3.11	0.56	3.02	0.63	0.20
Intention to comply with the law	5.69	1.73	5.87	1.61	0.39
Maintenance self-efficacy	3.42	0.79	3.37	0.81	0.64
Recovery self-efficacy	3.51	0.81	3.52	0.73	0.92
RR perception	−0.46	1.25	−0.47	1.28	0.96
Absolute risk perception	0.14	1.26	0.18	1.36	0.77
Perceived risk of breaking the law	3.29	1.94	3.53	1.86	0.29

Factors within the best fitting model (model B) are printed bold. Exposed: people who answered at least one of the questions on campaign exposure with ‘yes.’ Unexposed: people who answered all questions on campaign exposure with ‘no.’
PSM, propensity score matching.