Year	% of total
1970	66.97224636121209
1971	65.82019674839688
1972	65.65567875707255
1973	65.35269440749663
1974	66.77097053980773
1975	65.69302493424581
1976	64.53960251505154
1977	63.03795855269604
1978	62.01793583817848
1979	60.711042530080064
1980	60.226884057942506
1981	58.27952910294128
1982	57.326324913941406
1983	55.87974777143838
1984	54.95667582654305
1985	53.529063058379066
1986	52.8758666754783
1987	51.65448004715564
1988	51.081869635957354
1989	49.86910813242385
1990	43.96632366697848
1991	43.342776203966004
1992	42.37605238540692
1993	42.52553389043639
1994	42.02370100273473
1995	42.119565217391305
1996	41.81494661921708
1997	42.0911528150134
1998	41.14035087719298
1999	41.00529100529101
2000	40.909090909090914
2001	43.24577861163227
2002	43.258426966292134
2003	42.76377217553688
2004	43.11926605504588
2005	42.318307267709294
2006	41.95612431444241
2007	42.988084326306144
2008	42.71217712177122