Year	% of total
1970	53.41068723320227
1971	50.49318591778745
1972	48.38623727266316
1973	47.30477955674042
1974	47.959231261774356
1975	46.274444339468914
1976	44.53221869241153
1977	45.286318724806144
1978	44.57619233319973
1979	48.82578491250854
1980	50.312181912468546
1981	50.58537941172684
1982	51.48391408215611
1983	52.65314215444329
1984	50.995809509483244
1985	48.68262382209573
1986	50.932564812700996
1987	31.40689816083066
1988	34.27713680082482
1989	35.437249322820804
1990	11.572226656025538
1991	10.975157582499072
1992	10.055671537926235
1993	7.545909849749583
1994	7.603254067584481
1995	7.680988816951148
1996	8.139876579488686
1997	8.541238626357499
1998	9.369527145359019
1999	8.997353719494267
2000	8.865248226950355
2001	8.196221815965874
2002	8.857231340972438
2003	9.940420194418314
2004	11.329113924050633
2005	12.580025608194623
2006	13.409596441054973
2007	14.118761844598863
2008	12.713228194399742