Year	% of total
1971	16.664480315081192
1972	17.201498388502653
1973	15.92940464392906
1974	16.451413120357586
1975	16.08430087011211
1976	17.10165254886257
1977	16.384572812216035
1978	15.243304652798145
1979	14.810924074765493
1980	14.878624024330492
1981	15.574157443143783
1982	16.389765025035498
1983	16.49601387496144
1984	17.30088739948045
1985	19.362716188891195
1986	20.599793736664505
1987	22.337256407531182
1988	22.092791803277237
1989	22.46772551439518
1990	33.58977758536588
1991	34.36895071239083
1992	35.10548593025963
1993	35.0540857346554
1994	34.481178877370105
1995	35.48077739711045
1996	34.93911452001798
1997	34.98863549529148
1998	34.58101055959886
1999	35.389852597046044
2000	36.234133661913944
2001	36.691909493919226
2002	36.58750022811147
2003	35.58859807328468
2004	34.59877395010844
2005	34.53733734882095
2006	35.572552219172934
2007	35.63914604147582
2008	36.457611658698255
2009	36.37487612922577
2010	36.5802979039112
2011	37.48796060347373
2012	40.169044592075096
2013	41.16687587653246
2014	42.502030255803405
2015	43.809407248264854