Year	% of total
1971	32.62733737786781
1972	33.72894205743586
1973	33.52456000300515
1974	33.76758000729807
1975	33.64162682871635
1976	33.92765785028
1977	34.38481597817303
1978	32.62112800592449
1979	33.5996433661344
1980	34.37775330988634
1981	35.066619700204946
1982	37.12521105247756
1983	38.48149760325027
1984	38.98734705607877
1985	40.6747570368026
1986	40.73842299990777
1987	43.267223328289525
1988	42.43905640065827
1989	42.54592832892455
1990	69.3673004910265
1991	69.62124296618111
1992	69.8989239575759
1993	69.89671793386573
1994	69.58070654986457
1995	71.5518256442859
1996	71.52906040790762
1997	72.56874448967255
1998	72.42984295119858
1999	73.5308905656477
2000	74.5775467882284
2001	74.6557314495719
2002	75.75310652371017
2003	75.17118375485109
2004	75.18046510339337
2005	74.48356611260775
2006	74.28811196597484
2007	74.95849731835659
2008	76.34707329097351
2009	76.97451292487125
2010	76.37568609786692
2011	75.99681299152532
2012	76.71421480316923
2013	76.03002531716724
2014	76.81862540489979
2015	77.88678784872994