Year	% of total
1960	31.555315345279176
1961	32.16483160621762
1962	33.62052312328556
1963	35.32358172117164
1964	36.683603082203305
1965	39.635625075785136
1966	39.08578394027123
1967	40.137868429264415
1968	41.602200915232075
1969	43.287621797185125
1970	46.24155405405405
1971	47.13647928568
1972	45.320977018185204
1973	48.01629852026593
1974	44.54278541338667
1975	44.343674422483524
1976	42.189111265441845
1977	41.5153290372974
1978	40.36667271737157
1979	38.89097509074978
1980	37.27864713113392
1981	37.222222222222214
1982	36.36306680241209
1983	34.20036180511416
1984	34.43583384996901
1985	29.834002188982122
1986	30.840935833371535
1987	29.836342549505307
1988	29.58927192304992
1989	29.34164147381484
1990	31.411555386949924
1991	29.682599448453022
1992	30.090552615889106
1993	32.16366683800852
1994	31.468273585244198
1995	30.008725303622715
1996	31.3259891852198
1997	29.153588356097405
1998	26.61109869987182
1999	26.768087016574587
2000	26.854462383046545
2001	23.36521915584416
2002	25.487878942446656
2003	27.140738089150258
2004	26.04356065376297
2005	26.90482990988065
2006	26.16939209726444
2007	25.699544852998418
2008	27.56149292149292
2009	27.208870743132042
2010	29.6389404930941
2011	30.955194805194804
2012	31.758423412914432
2013	32.53958525588631
2014	32.49619498215638
2015	31.167110407745298
2016	30.969322064798416