Year	% of total
1970	31.848380160657484
1971	30.91522464562652
1972	30.700242105376375
1973	31.88330683020081
1974	33.15870886902021
1975	34.4888984993129
1976	36.42279324407581
1977	38.04195972789722
1978	39.24187308307571
1979	38.51840377176409
1980	39.55584863713837
1981	40.878288134639725
1982	42.051941156996534
1983	43.074126533967444
1984	44.26926486530845
1985	46.009611199187546
1986	47.24543287198731
1987	47.99455876173146
1988	50.93948013615891
1989	51.39718810830413
1990	74.60136674259681
1991	75.57527030773497
1992	78.66473149492018
1993	85.10996631662374
1994	82.14703816436432
1995	82.45654162854528
1996	83.21224991617302
1997	81.47963009247688
1998	80.45142555438225
1999	81.61215239495283
2000	84.68934911242604
2001	85.11571006218779
2002	85.13922518159806
2003	85.25158478605388
2004	84.17122946739671
2005	84.09244753892273
2006	85.48305513404148
2007	85.02798897150974
2008	84.80847595762022