Year	Percent
1971	21.03947
1972	21.28235
1973	23.19448
1974	23.66886
1975	27.65417
1976	28.83904
1977	37.43512
1978	41.81793
1980	53.25502
1983	48.61044
1985	58.56043
1986	57.13275
1987	53.42975
1988	58.1129
1989	53.70081
1993	54.03466
1999	51.11945
2000	50.4104
2004	68.02437
2007	56.6427