Year	% of total
1970	25.69177822885866
1971	24.32163112346443
1972	25.64892596171641
1973	19.854798238388103
1974	19.44394296261413
1975	18.095488384699348
1976	18.21700629113783
1977	17.440679141211636
1978	15.803218504387157
1979	16.488776086334845
1980	16.815361710931484
1981	17.890307923907496
1982	18.60106594796272
1983	19.176093632810392
1984	18.5915860035823
1985	19.17421456859091
1986	18.888791395242137
1987	18.023308188879017
1988	16.045001437028027
1989	17.077704059942032
1990	11.072158924919663
1991	10.716365754222481
1992	11.455641688199828
1993	11.036886436247459
1994	10.530846484935436
1995	10.005668934240362
1996	9.828349944629014
1997	9.331218609569126
1998	8.716075156576201
1999	8.594150846587993
2000	8.616780045351474
2001	8.5580014840465
2002	8.449669360764144
2003	8.809175207418253
2004	9.00834560628375
2005	9.102121361618156
2006	8.802992518703242
2007	8.661609982872523
2008	8.945362134688692