Year	% of total
1970	23.78761310913564
1971	24.382899349847122
1972	24.524205478501234
1973	23.975928830521894
1974	26.27316408982895
1975	25.911730207267127
1976	25.707193412797874
1977	24.965507861656548
1978	26.44489386121273
1979	26.944167951205934
1980	26.549189499375885
1981	28.735882936576363
1982	27.066346688463966
1983	27.73770217256037
1984	27.893830959165577
1985	29.138474925584767
1986	28.8417523247834
1987	31.665704364124426
1988	31.431981950402815
1989	29.927221226728403
1990	38.05220883534137
1991	37.70651117589893
1992	37.94089609151573
1993	37.79015784586815
1994	39.02439024390244
1995	39.96447602131439
1996	40.53826745164003
1997	40.58313632781718
1998	40.161527165932455
1999	42.05946337926033
2000	42.737430167597765
2001	42.944785276073624
2002	42.725477287689266
2003	41.07142857142857
2004	41.71741778319123
2005	40.37909247558874
2006	44.815668202764975
2007	44.32882414151925
2008	38.94957983193277