Year	% of total
1971	35.64006402547822
1972	35.57440051745956
1973	35.23012551688635
1974	34.213681542997946
1975	34.42332428473495
1976	33.935858354637574
1977	34.12824463039122
1978	34.55249957079627
1979	34.367746556765006
1980	34.32313411177804
1981	33.88793529630617
1982	34.1828201636363
1983	34.303906221240474
1984	34.253238145700905
1985	34.62455825026574
1986	35.064064228968014
1987	35.86937387096909
1988	35.428234525526456
1989	35.90291297968384
1990	69.44470043182599
1991	69.60058096549699
1992	69.38466103692457
1993	68.3913766340979
1994	68.08214901629577
1995	68.00887088323783
1996	68.48500988460847
1997	68.94440784912496
1998	68.96373295774887
1999	69.62578650009382
2000	70.26044797439106
2001	70.46802418924509
2002	71.09617696259257
2003	72.13831203353678
2004	71.94238427602538
2005	72.1531750300747
2006	72.68934474864145
2007	73.68470387025724
2008	73.4643852405197
2009	73.33336084180313
2010	73.12550548327879
2011	73.98427998495383
2012	73.04618674735912
2013	72.8402786889454
2014	72.11270181305385
2015	71.36460555457288