Year	% of total
1971	1.9158178200469742
1972	1.7862280914800381
1973	1.7776972467473358
1974	1.6429140536199185
1975	1.8821100097279064
1976	1.7817499041385494
1977	1.6373029110137292
1978	1.584640614469389
1979	1.8432607176209204
1980	1.7301888944389165
1981	1.553809660509196
1982	1.9020544031396351
1983	1.7883011918046254
1984	1.7904631523051149
1985	2.100546825997651
1986	2.0645828531413737
1987	2.3143869243840554
1988	2.954084502274024
1989	3.2833313031706854
1990	23.270912450393187
1991	22.726306235463316
1992	21.356820390192002
1993	20.087851356109752
1994	17.788314927718194
1995	17.23600177532888
1996	17.363639522293145
1997	17.547774365540988
1998	17.377647551847485
1999	18.11113709349608
2000	18.4034458458067
2001	18.787664481900606
2002	18.53111844958681
2003	18.67001983171416
2004	18.216677941661036
2005	17.943940595956633
2006	17.60921484589355
2007	17.45338277603665
2008	17.715409545491866
2009	17.10282357483704
2010	17.101841666483924
2011	15.77817283689758
2012	15.880728545073937
2013	15.587705109236857
2014	15.793339033990792
2015	15.850566709201566