Year	% of total
1960	55.54943510092918
1961	59.06735065361396
1962	62.65811009288485
1963	60.77492938282849
1964	66.14961043193367
1965	63.42359501802057
1966	61.37655211108085
1967	64.81712735849314
1968	66.05046166441429
1969	67.52914132549557
1970	69.6526025289658
1971	73.1362452097565
1972	72.90422640494424
1973	74.8880435201345
1974	73.18007570400013
1975	70.91456099633866
1976	75.1272800872157
1977	67.81770743545475
1978	68.84137772956778
1979	67.97404083158453
1980	67.70852294763034
1981	63.34484085871108
1982	61.825733111207356
1983	59.221159731333884
1984	54.51608317211388
1985	51.116433460025945
1986	49.92285080163157
1987	49.38574430924148
1988	47.55875619826941
1989	50.45988606008528
1990	51.166601960427286
1991	50.587586315040824
1992	49.43200742955444
1993	47.67219624225565
1994	47.94423403969042
1995	48.70329408443176
1996	47.651591477875904
1997	47.98396231855405
1998	49.286267266084465
1999	49.26414876266551
2000	49.02686607630417
2001	48.06822565800123
2002	49.891072645971626
2003	50.32416338617711
2004	49.9323706643215
2005	51.09850099191112
2006	50.41169432052692
2007	51.18173244669407
2008	49.71810788676991
2009	48.106245556421136
2010	46.40095173902687
2011	46.29299656443078
2012	44.921500754500585
2013	41.4664597170335
2014	38.963659272078175
2015	40.67540116429672