Year	% of total
1971	16.31131406625908
1972	16.52963244959362
1973	16.647273525383323
1974	17.448180110939234
1975	17.164345506343512
1976	17.28117206033575
1977	17.527734316998753
1978	17.1935536026652
1979	17.429737431313995
1980	17.717565483433027
1981	18.139685606935426
1982	18.034491649582257
1983	17.846441762160826
1984	17.85247267443717
1985	17.677461678957286
1986	17.385547465002766
1987	16.97670813385959
1988	17.376635211747125
1989	16.92796923978522
1990	22.468524879799222
1991	22.866852619770984
1992	23.06560228355717
1993	24.1542327375097
1994	24.881140655053567
1995	24.945201055713085
1996	24.149721108533324
1997	23.983193889182356
1998	24.333272427602296
1999	23.4637408652725
2000	22.813547838532585
2001	22.444344380034075
2002	21.74847820677355
2003	20.469261854744385
2004	21.198739187347922
2005	21.27514336459001
2006	20.81679870291276
2007	20.00140686911346
2008	20.16536613848029
2009	20.143918017575277
2010	20.03792361648877
2011	18.888624498891513
2012	19.425696411930506
2013	19.214005646490207
2014	19.38419585843717
2015	19.100051622875473