Year	% of total
1960	67.36429038587313
1961	61.22492080253432
1962	55.04322766570605
1963	57.21449369136202
1964	54.56697298802562
1965	51.82755388940956
1966	50.35452749041032
1967	44.88077007219427
1968	42.27001918610522
1969	41.68950203156005
1970	41.03027175782594
1971	37.11300606898671
1972	35.12630217198883
1973	32.375785969670815
1974	32.647552783109404
1975	31.993748604599244
1976	32.073219259848784
1977	29.368397392672513
1978	26.452439719005127
1979	33.139252789907815
1980	31.958762886597935
1981	34.13368836654118
1982	35.831717393137176
1983	38.30140537037788
1984	40.56806002143623
1985	43.89045426431173
1986	44.71983434774424
1987	42.75108677242703
1988	42.56931339817099
1989	42.18519688355443
1990	47.316468898146816
1991	47.91424280350437
1992	44.682919975972766
1993	39.9805024738161
1994	40.52924770999805
1995	38.48323190300725
1996	39.596481531410085
1997	42.32610930316649
1998	44.0418333763219
1999	40.493475397936436
2000	40.26217708429508
2001	36.85911618970574
2002	36.52904285988853
2003	37.56516563241467
2004	38.23247506678539
2005	37.26917790732309
2006	39.26550959439274
2007	39.43259092639374
2008	39.914375696378826
2009	41.50361637077442
2010	41.29324380721594
2011	41.14237347349868
2012	40.52788737533447
2013	39.71613288493573
2014	40.76501761390324
2015	37.82353167041156
2016	39.5363274513468