Year	% of total
1971	12.884615384615383
1972	15.180935569285085
1973	15.96925704526046
1974	17.831893165750195
1975	19.15367483296214
1976	20.264623955431755
1977	24.0251572327044
1978	25.857059848925047
1979	28.210757409440173
1980	32.365657813465106
1981	34.07325194228635
1982	30.76470588235294
1983	33.29538986909505
1984	34.035476718403544
1985	34.45945945945946
1986	38.084874863982584
1987	40.58759521218716
1988	38.4180790960452
1989	42.74809160305343
1990	47.55517092167892
1991	41.12478031634446
1992	45.85406301824212
1993	41.720105620520556
1994	51.84135977337111
1995	56.67439549519708
1996	54.53983940704138
1997	53.5426267281106
1998	56.71159029649596
1999	52.64107188868849
2000	48.47938144329897
2001	45.15075376884422
2002	46.05640535372849
2003	52.88550323176362
2004	51.293389343356175
2005	58.74183006535948
2006	58.13207547169811
2007	58.30136030694105
2008	58.621282447997245
2009	60.51298807384414
2010	66.04692341744135
2011	65.803324099723
2012	67.6935125962668
2013	67.82393056416615
2014	71.99314677327241
2015	68.59756097560977