Year	% of total
1971	58.815987023246606
1972	53.471574400824586
1973	48.70325222328054
1974	47.72917722265598
1975	47.79083607952959
1976	43.413275788932296
1977	48.382180372110106
1978	51.518795042201525
1979	48.49453240448969
1980	45.38912229154093
1981	44.96107473537523
1982	46.12239293701823
1983	46.31933340227164
1984	49.06894426949685
1985	54.83536073212703
1986	57.81891896932419
1987	59.22624579049326
1988	59.229808775493964
1989	59.935926867307664
1990	60.96288007521594
1991	63.008570595252756
1992	64.21943105940488
1993	62.53481600378335
1994	63.33038894911469
1995	62.02110258042454
1996	63.86252973655768
1997	64.1123138693877
1998	63.693195128977834
1999	65.73039808944345
2000	66.89810574628665
2001	65.78208981480033
2002	67.20337739219877
2003	69.510436619766
2004	69.00122586731804
2005	70.48968345540561
2006	72.25631108031692
2007	73.50708705701966
2008	71.50193055039496
2009	71.23856453571365
2010	70.61955757840379
2011	72.91158618766329
2012	70.22232315088958
2013	70.18523894472612
2014	67.80981050368317
2015	66.06102628981188