Year	% of total
1960	47.49611846569681
1961	47.720656018193985
1962	47.852930470439205
1963	49.43677099495644
1964	49.08775264258196
1965	49.819889685049226
1966	49.18098801168899
1967	47.907391499866264
1968	47.843567319588615
1969	45.53353820361883
1970	43.120684733435894
1971	41.779811447280565
1972	41.335530442163446
1973	42.13445875297831
1974	40.12651125367101
1975	40.50587989254385
1976	42.184920149513786
1977	42.177149334648135
1978	40.19441077883904
1979	43.295258432545424
1980	46.49890168772547
1981	47.76162591668599
1982	48.64392488130521
1983	49.748671105233186
1984	50.66893640295172
1985	51.25975481018921
1986	49.99607048625857
1987	51.34518204766748
1988	51.716925056354846
1989	49.17782153033097
1990	48.34051808463302
1991	47.82961538967201
1992	48.29198144506485
1993	48.242804342084575
1994	47.38093916678238
1995	46.603378639103084
1996	47.68588447885983
1997	48.86510115717384
1998	48.383959737102245
1999	47.748177433923054
2000	48.5015775219014
2001	47.40346547015376
2002	46.60746554806105
2003	47.26830336478165
2004	46.146800033696934
2005	46.09542697095156
2006	45.44013530622885
2007	44.804276240397826
2008	44.740966030520234
2009	41.272234363568536
2010	41.810331364659184
2011	39.28977432549321
2012	34.78870854875243
2013	35.88207012616923
2014	35.65618997438402
2015	30.92854744716093