Year	% of total
1971	49.09164859002169
1972	52.015145498893865
1973	49.39282378152646
1974	53.51861029239156
1975	51.33486953890557
1976	54.14840767661978
1977	52.99409671680414
1978	48.32060583497535
1979	49.87635280665834
1980	51.04435714938253
1981	53.45953298571753
1982	56.81924202372033
1983	57.277304287735696
1984	58.1204437954166
1985	62.35772707242888
1986	63.686504454064554
1987	68.86419152177244
1988	67.40176817288801
1989	68.05104886357783
1990	65.46363226432368
1991	67.06780765279274
1992	68.0382346573502
1993	70.05334700494672
1994	67.7073178220786
1995	69.93626965019119
1996	70.4767837916534
1997	68.93212715633052
1998	66.79569866858826
1999	66.9578760283636
2000	68.4994242462541
2001	69.41705728436118
2002	69.89346472247429
2003	67.83142322885762
2004	67.69168015368624
2005	66.85963647338944
2006	66.68824891701043
2007	65.4820578389267
2008	68.44469591149931
2009	66.96802143677873
2010	67.1782980878401
2011	66.75997826038402
2012	71.63605506082104
2013	72.52273811203138
2014	74.49218586947953
2015	75.30939896052361