Year	% of total
1971	24.16400604940346
1972	25.858778625954198
1973	24.93993993993994
1974	24.656404617921936
1975	23.406813627254508
1976	23.72410308236483
1977	27.33913043478261
1978	26.89411227749886
1979	25.885146804835923
1980	29.269265277639317
1981	24.925595238095237
1982	24.65620592383639
1983	22.74854896086875
1984	24.806596956558703
1985	21.13780860374866
1986	21.115230151374732
1987	21.362273311437953
1988	22.08530106257379
1989	22.401107306767685
1990	23.196697566628043
1991	19.72793813009253
1992	25.148605395518974
1993	19.58400864397623
1994	18.908357494012353
1995	19.703914767096133
1996	22.07040296433534
1997	25.575305064913355
1998	25.00672947510094
1999	22.93067226890756
2000	18.012453550266144
2001	14.476850514967754
2002	17.085930036846655
2003	18.29087419298552
2004	27.11193568336425
2005	27.730499235264126
2006	26.70516850646977
2007	33.28990010357155
2008	39.86740672217083
2009	39.40903155273467
2010	42.27918640289774
2011	43.23993575198226
2012	44.74968100277715
2013	46.06031351997426
2014	47.63154441674321
2015	47.26948664276388