Year	% of total
1971	10.900216169264972
1972	13.228543040360236
1973	17.710352876623425
1974	19.625945521159533
1975	21.221046795516642
1976	21.875112944897914
1977	20.151470329896718
1978	18.17904639598752
1979	21.764244654859453
1980	23.406265453187235
1981	22.784219666444088
1982	25.9362888749769
1983	22.008698742450054
1984	24.200788966090567
1985	23.93745180979331
1986	23.690979137470134
1987	30.057070098659572
1988	32.32822451753221
1989	35.470084700645025
1990	40.52976358501994
1991	41.94531152044393
1992	43.00962328313044
1993	45.74401195698427
1994	48.640147755083206
1995	48.59668068617115
1996	49.04053512438684
1997	49.81716973430931
1998	51.972494045008744
1999	55.437264999612566
2000	54.720032037525456
2001	57.34502184128837
2002	57.997515316952054
2003	61.08560884875865
2004	61.14814288559314
2005	63.12022663949899
2006	63.055477582179265
2007	63.46288147084492
2008	66.3548511519851
2009	66.93589087523785
2010	66.6743345489347
2011	64.11702386195397
2012	63.425130144573906
2013	59.72045598165262
2014	62.932868573767124
2015	67.06377333076605