A Survival Analysis on Fuel Cell Technology Patent Maintenance and Values Exploration between 1976 and 2001

Table 1

Renewal and citation records of the fuel cell technology patents.

Renewal	Citations
	0	1	2	3	4	5–10	11–15	>15
0	128	21	7	3	3	21	10	8
1	49	40	21	21	19	42	16	18
2	2	4	4	10	7	24	6	32
3	3	4	8	13	4	28	16	21