Year	% of total
1971	14.035300128610055
1972	14.046582027432247
1973	14.688728946511503
1974	14.49894204106769
1975	13.334986739092338
1976	13.81864856723502
1977	13.759674029632203
1978	13.881189158712058
1979	14.051745918274595
1980	15.01421062570148
1981	14.635416995790385
1982	14.821105035417329
1983	14.746527630858017
1984	15.025616786708891
1985	15.286778372023427
1986	15.823796537736095
1987	15.877072591435136
1988	16.57488983262806
1989	16.29153965849593
1990	16.91177214103155
1991	16.689742024340816
1992	16.544145008339147
1993	16.665719837683444
1994	16.932022824331515
1995	18.394352086904046
1996	18.723083018888516
1997	19.19517206138569
1998	19.333197996744694
1999	20.452975031159106
2000	20.31693550739839
2001	20.96264298884918
2002	21.06094525629639
2003	22.12353232737933
2004	22.915855011437277
2005	23.03770200617887
2006	24.269035009842042
2007	25.050987272244075
2008	25.637090541764582
2009	25.985342498113795
2010	26.495448089760085
2011	26.26947823906963
2012	27.12556910864409
2013	27.93096528660105
2014	28.224104890517353