Year	% of total
1960	67.09961093237008
1961	64.09146806938652
1962	60.7852492141895
1963	58.88048569858425
1964	57.11365150971446
1965	55.74380812284592
1966	54.61808796881006
1967	52.67535959416668
1968	50.735630892240835
1969	49.4270462924361
1970	50.09528339426497
1971	48.18710898141856
1972	47.19807280960923
1973	45.76394507146424
1974	44.19378232212704
1975	43.32138441161039
1976	42.85707556612772
1977	42.13464337202867
1978	40.51660930966834
1979	40.26105327517592
1980	40.82177794537657
1981	37.77369508031387
1982	37.600755713824874
1983	36.8417508696544
1984	36.33705470352582
1985	38.39270329678698
1986	39.3740340030912
1987	39.639309042627715
1988	39.06025328864008
1989	37.973598393688675
1990	57.08820127767488
1991	51.496432647495595
1992	30.745727749161027
1993	30.22946629413928
1994	32.06007533155183
1995	31.82315815707074
1996	32.847131349470146
1997	31.782842277129202
1998	30.14803378192611
1999	31.53823981045909
2000	31.173069754951328
2001	29.967434603798647
2002	30.043087040463355
2003	29.549632700254243
2004	28.556620277422883
2005	28.326577914230654
2006	28.261283889591155
2007	26.93793761899077
2008	28.13842946055519
2009	24.652682036156424
2010	24.923583276485004
2011	24.10080792884738
2012	27.407572381603735
2013	25.963124099456902
2014	25.194964153691046
2015	29.09034516189094
2016	28.85286334835718