Table 4

Results of sensitivity analysis: costs, benefits, and benefit:cost ratios (BCR)

	Age 5–12			Age 13–18			Adults
	Costs of law ($)	Value of benefits ($)	BCR	Costs of law ($)	Value of benefits ($)	BCR	Costs of law ($)	Value of benefits ($)	BCR
*Base case: cost of helmet = $19.95; life of helmet = 5 years; discount rate = 5%; no quitters; head injuries averted per year: 4.0 5–12 years, 10.3 13–18 years, 28.8 adults; treatment costs: $1569 5–12 years, $1607 13–18 years, $1351 adults; societal cost of serious head injury = $196360; societal cost of minor head injury = $13309.
Base case*	180792	471920	2.61	1507312	1279050	0.85	5819397	4289602	0.74
Cost of helmet: $50.00	453769	471920	1.04	3761912	1279050	0.34	14791731	4289602	0.29
Cost of helmet: $10.00	90580	471920	5.21	756834	1279050	1.69	2918097	4289602	1.47
Life of helmet: 7 years	180792	629156	3.48	1507312	1703263	1.13	5819397	5703009	0.98
Life of helmet: 3 years	180792	298307	1.65	1507312	813948	0.54	5819397	2735117	0.47
Law enforcement costs	287727	471920	1.64	1760586	1279050	0.73	6564065	4289602	0.65
Discount rate: 10%	180792	426669	2.36	1507312	1160630	0.77	5819397	3898996	0.67
Discount rate: 0%	180792	522489	2.89	1507312	1416873	0.94	5819397	4771906	0.82
Head injuries averted: upper CI	180792	1180572	6.53	1507312	1733409	1.15	5819397	5295651	0.91
Head injuries averted: lower CI	180792	0	0	1507312	829022	0.55	5819397	3317056	0.57
Costs of head injury increase 20%	180792	565879	3.13	1507312	1537458	1.02	5819397	5179263	0.89
Costs of head injury decrease 20%	180792	377855	2.09	1507312	1024972	0.68	5819397	3433444	0.59
Numbers of quitters	76697	2445747	31.89	670778	8887908	13.25	4349481	15258505	3.51
Cost of quitting: $19.95	193803	2445747	12.62	1611879	8887908	5.51	6003137	15258505	2.54
Cost of quitting: $49.95	369903	2445747	6.61	3027069	8887908	2.94	8489837	15258505	1.80