Year	% of total
1970	54.849382384265475
1971	57.37825460302951
1972	56.453335446269236
1973	53.558626129039844
1974	50.02629399241337
1975	51.96361194209537
1976	53.07069961848031
1977	52.05607480223726
1978	51.0301349584331
1979	50.811849431374426
1980	50.24972668075004
1981	48.53179216608217
1982	52.56532275786115
1983	52.78145702157718
1984	54.69064822357604
1985	55.383426082151765
1986	57.510652358558964
1987	58.84246262231869
1988	60.29230815981861
1989	59.078178154213745
1990	74.14589104339797
1991	75.20344662517951
1992	73.96265560165975
1993	76.02015113350126
1994	74.13541159279103
1995	72.32055063913471
1996	74.25389755011136
1997	73.56529597830999
1998	75.03195568811249
1999	73.6081597960051
2000	73.78435517970402
2001	75.23056653491436
2002	75.66964285714286
2003	77.23577235772358
2004	77.31092436974791
2005	74.29511278195488
2006	75.1959428307976
2007	76.07030193780983
2008	73.69207772795217