Year	% of total
1970	6.152670086423686
1971	6.284378937595503
1972	6.491556537611267
1973	6.395769994283647
1974	6.910088948432468
1975	7.083230442980819
1976	7.1795356153706855
1977	7.009610873789033
1978	7.374984156178507
1979	7.363164692874504
1980	7.17638224543075
1981	7.619481403284993
1982	7.4803702028897145
1983	7.638337962492317
1984	7.97294244536059
1985	8.056586974893307
1986	7.89787139357057
1987	8.34044927614171
1988	8.639146195904043
1989	8.425183547237197
1990	10.201573254670599
1991	13.047596495382429
1992	15.488215488215488
1993	19.761620977353996
1994	21.98532783127006
1995	24.116470326739275
1996	24.963165649336982
1997	25.873844917637605
1998	25.712171661117278
1999	27.29601170874497
2000	29.770136423098485
2001	29.22718307333692
2002	27.098243331164607
2003	28.134809185527835
2004	28.235103101152788
2005	27.773431387889218
2006	27.140309155766946
2007	25.610921501706486
2008	25.275590551181104