Year	% of total
1971	61.6473158093651
1972	61.62023859950534
1973	62.13705357984691
1974	59.596606104450785
1975	58.43021371558223
1976	59.58709472642717
1977	58.953991922650715
1978	57.858828421307074
1979	57.72569261699276
1980	57.65225074513085
1981	56.26620682260065
1982	55.03176583735014
1983	54.046367817421036
1984	53.20052286689957
1985	52.06034396722855
1986	51.44452444458497
1987	51.83488261547326
1988	51.59433445295352
1989	52.39336628893151
1990	61.90984222680973
1991	61.705708985727625
1992	61.70576735835387
1993	61.163262674286344
1994	61.25417369627545
1995	60.985053743517334
1996	61.21843560797614
1997	62.01618828738097
1998	62.538826000785456
1999	62.84873907267175
2000	63.649455740310714
2001	64.05200119626078
2002	64.57904495804763
2003	65.79040889537046
2004	65.4593295903228
2005	65.72091020659958
2006	66.04763621225449
2007	67.16657889922934
2008	66.79040104814598
2009	66.07813805004574
2010	66.27537574700276
2011	66.95639240153339
2012	66.7861909471609
2013	66.28235613494044
2014	65.59679137340325
2015	65.19955768666729