Year	% of total
1970	37.51702532691968
1971	39.19160186389756
1972	39.02119498622522
1973	39.531796975046525
1974	40.82071466787528
1975	41.33362402018484
1976	40.84204649496482
1977	40.8393856104298
1978	41.876182255254655
1979	42.42111315474805
1980	42.6513753367147
1981	43.024407952596036
1982	42.96421255376193
1983	44.17740028686537
1984	44.334060393051026
1985	44.11507056639848
1986	45.3890855108386
1987	47.63091704011995
1988	50.61636492575483
1989	51.267023601951
1990	58.80574452003023
1991	58.85885885885885
1992	58.675799086758
1993	59.150579150579155
1994	58.782742681047765
1995	59.115179252479024
1996	59.399075500770415
1997	59.076682316118934
1998	59.537110933758974
1999	61.904761904761905
2000	61.88118811881188
2001	63.87931034482759
2002	64.31797651309846
2003	65.48076923076923
2004	65.14118792599805
2005	65.9
2006	66.02434077079108
2007	66.80497925311202
2008	67.83068783068784