Year	% of total
1971	0.8710801393728222
1972	0.5524861878453038
1973	0.5196733481811433
1974	0.4768392370572207
1975	0.5225342913128674
1976	0.4857316332726169
1977	0.5681818181818182
1978	0.4155844155844156
1979	0.4506760140210316
1980	0.44923629829290207
1981	0.42283298097251587
1982	0.4058441558441558
1983	0.34843205574912894
1984	0.3260515161395501
1985	0.35511363636363635
1986	0.339097999321804
1987	0.31918289179699966
1988	0.31318509238960224
1989	0
1990	0
1991	0.2587991718426501
1992	9.873778501628665
1993	9.873778501628665
1994	9.873778501628665
1995	9.936488424503176
1996	11.328613077884214
1997	11.263589378007484
1998	12.65472011823388
1999	14.713499514405957
2000	16.996675820205233
2001	17.59822090437361
2002	19.04318936877076
2003	17.093787736481953
2004	18.08886183810103
2005	17.227602905569007
2006	17.971714384270438
2007	17.226519337016573
2008	14.893392442474141
2009	17.561761546723954
2010	17.531044558071585
2011	18.653376729048006
2012	20.748967957538824
2013	21.37762579384465
2014	24.048155035724772
2015	24.389567147613764