Year	% of total
1971	28.374251074907637
1972	30.901650284835636
1973	32.740063235220575
1974	31.20848490178167
1975	30.959266440187218
1976	27.182841496805594
1977	27.056915375149547
1978	26.57063279810513
1979	26.125850138341306
1980	24.07761316800545
1981	21.09116173835471
1982	19.969838455364616
1983	20.787973023840095
1984	20.846520249591702
1985	23.481009715959274
1986	27.248221442720915
1987	29.24177875489673
1988	30.703212170448296
1989	31.977121765150766
1990	31.43620294153508
1991	36.7077056159674
1992	38.14089543683896
1993	41.63508769576894
1994	44.51157972847883
1995	46.74147468456184
1996	43.12577744285668
1997	47.65365459025724
1998	49.22261006433874
1999	46.52849402065575
2000	44.93850095850028
2001	44.19638328809734
2002	44.20870069090163
2003	45.02381534505085
2004	44.534086767063116
2005	44.0880532026738
2006	44.29105096338574
2007	47.82811691982863
2008	44.61572393773462
2009	47.22862760011262
2010	46.45622974448939
2011	47.381766794729046
2012	48.464304699367254
2013	47.89684352291182
2014	48.42958734087677