Year	% of total
1970	39.93595608098005
1971	40.017395706685086
1972	39.74620987793852
1973	40.51357485626127
1974	39.48770527514643
1975	43.62763912325342
1976	41.30624159573553
1977	40.56517402351829
1978	40.598271088883905
1979	40.7353463153633
1980	41.70339724494331
1981	42.44751121672371
1982	44.06575354345646
1983	42.9861622525986
1984	43.544145122857365
1985	43.00077595124878
1986	42.30930498773507
1987	41.57678022102233
1988	38.79011604641857
1989	40.53832867963016
1990	64.50914340712224
1991	64.10819005066422
1992	64.39827244076106
1993	63.51273921845754
1994	63.57336100507727
1995	62.00447394477246
1996	62.22230159297093
1997	63.41926531804572
1998	64.41299596191605
1999	64.90295835688713
2000	64.48085349590397
2001	65.84849435382685
2002	65.76544806238
2003	66.80765977082211
2004	67.7256038647343
2005	66.88248749660761
2006	67.55603398562147
2007	67.84534163849747
2008	70.78882663549518