Year	% of total
1971	16.819013741911732
1972	17.936167572370177
1973	18.942459559948688
1974	19.360463015719958
1975	19.424224900538324
1976	20.206219616966976
1977	21.10587753080546
1978	21.535332342465427
1979	22.320400792720882
1980	22.85745822205444
1981	23.73540180643755
1982	24.833250777932797
1983	25.01398927892393
1984	25.03624025799535
1985	25.25411041026731
1986	25.52696677015724
1987	26.96491173829311
1988	27.27967969146509
1989	27.607624178744185
1990	40.371759235488916
1991	40.65162900925437
1992	39.61881829428056
1993	39.45361661085405
1994	38.09476990839431
1995	37.675052261421044
1996	38.333057414069465
1997	38.59501152683131
1998	39.29632682086478
1999	40.05038226613929
2000	39.82817434697205
2001	39.93380828819246
2002	39.92883712110501
2003	39.88995489655621
2004	39.88241517060029
2005	39.88316717751661
2006	40.036516533231286
2007	40.39391605770744
2008	40.53657371927891
2009	39.09477225377385
2010	39.06104079740709
2011	36.7610610690494
2012	36.80912868586531
2013	37.595116318817524
2014	33.450471838459386