Year	% of total
1971	26.86599840639463
1972	21.61648020112908
1973	21.706115576901297
1974	18.302446257613095
1975	17.220214356386183
1976	15.593061885314835
1977	15.396052739936572
1978	16.509170967491848
1979	17.408640729039323
1980	16.96831553128048
1981	17.129317477566456
1982	18.226946163113887
1983	19.803456770605283
1984	20.992393390302194
1985	22.53551560393849
1986	23.786433992807687
1987	26.945317762962024
1988	28.19830143373049
1989	27.652861243826727
1990	28.598985293770056
1991	29.52642783099277
1992	32.18010980318748
1993	32.179626226267104
1994	33.26852708387779
1995	36.234915969782264
1996	36.7015649807578
1997	39.03044015220233
1998	35.41067132419529
1999	36.29687176837457
2000	35.717276753801976
2001	34.89466198830532
2002	35.20026036805966
2003	37.29691033223821
2004	39.693010351017726
2005	39.529116076851004
2006	40.14710145705755
2007	40.2215081185027
2008	41.935118518660815
2009	40.95445023910561
2010	40.07767789981387
2011	39.47516454101107
2012	42.04734456428038
2013	42.14273802406577
2014	42.253911766796485
2015	42.99439919836328