Year	% of total
1971	1.4591946640164732
1972	1.3153570294256391
1973	1.4078113842706146
1974	1.5086148886813715
1975	1.6844986070899515
1976	1.7909000649134907
1977	1.7602467775080737
1978	1.7692270123744838
1979	1.8426058406516959
1980	1.6649071785976737
1981	1.7510843458555962
1982	1.9240816431699863
1983	2.0686617217362984
1984	1.8834191618336202
1985	1.8059890205678046
1986	2.1003195511927295
1987	2.3157449038064213
1988	2.247343125640784
1989	2.226576063799741
1990	2.416534391682282
1991	2.62254824828717
1992	3.0352928136011963
1993	2.8619131413620558
1994	2.746596916251924
1995	2.711017001996335
1996	2.6903797987844076
1997	2.602724146132095
1998	2.4955885025785167
1999	2.5624340985781493
2000	2.5038227786016516
2001	2.775263992822212
2002	2.8794476247635927
2003	3.0122618092624047
2004	3.0499115359000526
2005	3.210951051849494
2006	3.1648895965616464
2007	3.5348089381011234
2008	3.414866897205674
2009	3.741195745428618
2010	4.70644955709272
2011	4.619941403989769
2012	5.190889494425498
2013	5.838479399258286
2014	6.90213517747588
2015	8.095143485481403