Year	% of total
1971	73.86544366909118
1972	74.0412039666417
1973	79.12931519004023
1974	77.8020921571562
1975	79.27448171498288
1976	79.11844590234985
1977	79.21392677772438
1978	78.92038598117485
1979	82.12486050650305
1980	83.71880866297965
1981	85.08556618540169
1982	86.85631640588943
1983	88.88393838392352
1984	90.06745531124092
1985	91.13962516249522
1986	90.95054255502332
1987	90.66508474288536
1988	91.58475905340862
1989	91.58156460108536
1990	86.86967751175378
1991	86.83219188457102
1992	86.36177247655547
1993	86.3614426831884
1994	87.20124210726762
1995	87.44171818056493
1996	87.3685274557244
1997	88.00868471367599
1998	88.1558803682707
1999	89.43253290749273
2000	90.41075399952312
2001	91.63693407392964
2002	92.42378635209536
2003	92.49369070580379
2004	92.74535115134913
2005	90.95402580754838
2006	90.72302119747204
2007	90.90713520743451
2008	92.48048841323065
2009	89.7557529353687
2010	89.02779354582941
2011	88.9277163799432
2012	89.34657003453069
2013	89.30308888391968
2014	88.7242587192851
2015	88.71404940891048