Year	% of total
1971	3.3451124491675333
1972	2.8882102439249127
1973	2.5964902454715677
1974	2.360404740732414
1975	2.109234309965912
1976	2.0199875403749785
1977	1.941132115772997
1978	2.2986603190395267
1979	2.1446782402261437
1980	2.203876412889057
1981	2.4815033502626416
1982	2.4950617033518423
1983	2.4851516804716502
1984	2.972306347666388
1985	3.148364564832825
1986	3.6107823547609352
1987	3.560102954759445
1988	3.769219010427956
1989	4.043570880507876
1990	3.9964518435067915
1991	3.9025140501981816
1992	3.593647206462995
1993	3.747093293659139
1994	4.1893759785821345
1995	4.475427440646797
1996	4.822221306581508
1997	4.815240664386152
1998	4.7053910816693465
1999	4.950596796607327
2000	4.497260136418687
2001	4.5835938659496245
2002	4.6440780263459995
2003	4.940926544210874
2004	4.506829648059153
2005	5.151158411184766
2006	5.198544434872901
2007	5.238897184062191
2008	4.398899041833478
2009	4.93318264847821
2010	5.282880765658352
2011	5.346044219904943
2012	5.883606889875061
2013	6.605951042374501
2014	6.664827260542036
2015	6.892445481184402