Year	% of total
1970	6.821814933818471
1971	7.044857627232274
1972	6.947303950127489
1973	7.349449726984012
1974	9.656732005524898
1975	9.08772117310714
1976	8.85629262048137
1977	7.919768472287125
1978	8.709227423316396
1979	8.898777186427838
1980	8.094454228902473
1981	9.143214130267726
1982	8.410924108694369
1983	8.723669229087887
1984	9.85876021365057
1985	10.26304958533982
1986	10.197795919423863
1987	9.87316869559956
1988	9.81798592347423
1989	9.10838691103971
1990	3.9647577092511015
1991	2.696629213483146
1992	2.658045977011494
1993	2.6206896551724137
1994	2.5759577278731833
1995	2.525252525252525
1996	2.349570200573066
1997	2.337228714524207
1998	2.3155627355950457
1999	2.224469160768453
2000	2.105755732335049
2001	9.653579676674365
2002	15.048543689320388
2003	19.420289855072465
2004	23.06930693069307
2005	25.878114680276195
2006	24.103172250222354
2007	22.03341013824885
2008	20.254596888260252