Year	% of total
1960	10.592557848655408
1961	9.517066626919064
1962	10.564774977805094
1963	9.751434034416826
1964	10.884177869700103
1965	12.321196358907672
1966	13.018932481751824
1967	12.281868040551768
1968	11.03111826836546
1969	11.177314834949767
1970	9.503695881731785
1971	8.760584515345315
1972	8.202135505178438
1973	6.807297289815353
1974	6.656271567700213
1975	7.323581495766926
1976	7.43069178227884
1977	9.246174617461746
1978	10.016995523130493
1979	9.811901238414206
1980	10.69188553508428
1981	11.489370784598309
1982	12.527421038059336
1983	14.370282344138552
1984	17.191640961028803
1985	19.25465838509317
1986	17.674607271922707
1987	19.403116938191324
1988	19.01425718989736
1989	18.67214940460893
1990	18.03166700292545
1991	20.000680865581437
1992	18.90264161794307
1993	18.795121758527745
1994	18.90961521192529
1995	18.386626501035195
1996	17.837046785850134
1997	16.93663955099286
1998	16.029567340762142
1999	16.039313086288338
2000	16.391080692103497
2001	15.84833427212417
2002	15.388964006555724
2003	16.932092451915306
2004	16.67297680254621
2005	15.980091676499955
2006	15.650463500808431
2007	15.744774408284023
2008	15.048928149183146
2009	12.68288857851381
2010	14.719446609508962
2011	15.382903241273493
2012	13.933073977333096
2013	14.256842770161123
2014	14.536162240025257
2015	15.515435548055088
2016	15.23359643366296