Year	% of total
1960	45.904344800453515
1961	45.730793725598836
1962	46.411171600536356
1963	46.599523247919535
1964	46.10258821795331
1965	45.59604340840948
1966	44.540841894885496
1967	44.29787383915219
1968	43.791082825737675
1969	41.558001637367994
1970	39.31007823172348
1971	38.85273818654386
1972	37.07209788814335
1973	37.263985522401846
1974	35.67653590156241
1975	36.02694075938437
1976	37.536424086875556
1977	37.30193648168101
1978	36.23502904156422
1979	37.706312189513625
1980	40.095046279047914
1981	40.27828281060168
1982	41.135443925147406
1983	41.71768253882604
1984	41.12391000388751
1985	41.95010427897327
1986	41.35467464139523
1987	41.6300949374043
1988	41.40912407710615
1989	40.34818938558794
1990	39.4413503437467
1991	39.084579049051804
1992	38.84857235641328
1993	38.560322303978715
1994	37.98523455788357
1995	37.53830256475636
1996	38.051311897148935
1997	38.00040856384841
1998	37.92835782232401
1999	37.30777342053604
2000	38.28077761401597
2001	37.68701180740587
2002	37.56454754699069
2003	38.27961726338037
2004	37.365022581736675
2005	37.09990795309482
2006	36.76048325325701
2007	36.43764243317351
2008	35.57484332842243
2009	33.77538247889268
2010	33.44675009455618
2011	32.63818259953727
2012	31.373042979197464
2013	31.70022431028212
2014	31.004641910476465
2015	28.58356459546038