Year	% of total
1971	56.417175035194745
1972	64.1370047011417
1973	63.82614647501711
1974	68.45218887813273
1975	73.15620705451214
1976	71.13290934569365
1977	71.28682487725041
1978	69.99034749034749
1979	66.89419795221842
1980	66.9815334865118
1981	68.0414092502922
1982	75.09055681913908
1983	76.14860583016477
1984	73.90531229162036
1985	78.84615384615384
1986	80.23602821486706
1987	82.0042207584575
1988	74.24179722140111
1989	59.193756667228115
1990	48.59568909209667
1991	65.79830669806121
1992	74.90050529893128
1993	74.374036578761
1994	67.19943031214147
1995	65.70093124487101
1996	54.79777437933166
1997	56.900021022914984
1998	44.90129263003745
1999	35.3998437092993
2000	46.19991017515844
2001	49.382803131833256
2002	50.983490187996615
2003	46.28328599799269
2004	42.92102796438056
2005	50.459187561923635
2006	52.655459146782356
2007	39.53237963390247
2008	40.52157309393005
2009	41.65870689371233
2010	35.93506966277261
2011	31.970842907796023
2012	28.899944086823126
2013	27.01293368918087
2014	32.27650001397311
2015	31.677875495775133