Year	% of total
1971	55.98336948662328
1972	59.81621192353509
1973	56.900104401340734
1974	60.76058321813297
1975	58.17680329585922
1976	60.156879150760865
1977	59.27240012938702
1978	54.65136340110235
1979	57.12766240327598
1980	58.84194703053759
1981	60.24786518552104
1982	64.3728530837845
1983	64.77804468722235
1984	66.23186972382055
1985	69.89510226454435
1986	71.13168048399037
1987	76.3392012114329
1988	73.92477079240341
1989	75.43834477481256
1990	73.41288277332167
1991	75.46201167714938
1992	77.25257354358638
1993	78.94525350219624
1994	77.33570787051607
1995	80.85540291743379
1996	82.18521954445626
1997	81.85170454305045
1998	80.93224628834483
1999	82.31434487054986
2000	83.44216483408462
2001	83.48184456561101
2002	84.76876406629299
2003	83.79363803840285
2004	83.0202444184207
2005	80.9492270029176
2006	80.01587006192943
2007	80.05155646866116
2008	81.70058525027848
2009	82.27508497746653
2010	81.23585892000948
2011	79.6323250221491
2012	81.28737036407138
2013	79.72050930684024
2014	80.89615531483008
2015	81.89209864902777