Year	% of total
1971	52.837748372289475
1972	58.15478442169427
1973	58.13786387237294
1974	61.589485127897404
1975	62.68302581563868
1976	64.32244946657573
1977	64.538815917038
1978	63.42471638325393
1979	62.53568181585894
1980	62.9824774371793
1981	62.828865484979815
1982	61.73478761568823
1983	60.1634942912466
1984	58.981030665997444
1985	57.44103971192196
1986	56.18042071398636
1987	53.02707361790214
1988	51.7815772839533
1989	52.332215328502095
1990	51.38991384296162
1991	50.47148032145814
1992	48.18277426763494
1993	48.18962347965564
1994	47.101839388878126
1995	44.52551138555545
1996	44.05800800075902
1997	41.728881996910246
1998	45.317323600498
1999	44.44894584178665
2000	45.18450673673744
2001	46.02766253006699
2002	45.666792549459316
2003	43.58638047543025
2004	41.20703927074026
2005	41.39431982276785
2006	40.88191971060904
2007	40.8067025223923
2008	39.08646112011075
2009	40.05631699580142
2010	40.887088275134104
2011	41.47396169570137
2012	39.07923570116205
2013	38.867959376571775
2014	38.70680567109987
2015	37.07298178866014