Year	% of total
1971	2.8659631724395407
1972	2.7675913131823724
1973	2.2364713840676775
1974	2.110837492603939
1975	1.978131564161991
1976	1.8207089695606637
1977	1.7439759486232993
1978	2.1308294331941577
1979	1.8723081800519534
1980	1.9187597841256157
1981	2.2607377290863933
1982	2.5357770406748448
1983	2.500291603359497
1984	2.8818425275626707
1985	3.198985282276206
1986	3.7857190176624047
1987	3.7671381303380733
1988	3.7211022769512243
1989	3.5501485302583102
1990	3.3179602869989604
1991	3.7215983819703786
1992	3.7369739383436227
1993	3.886346981734218
1994	4.106995601539106
1995	4.204729688883507
1996	4.1964060272919514
1997	4.276782606009528
1998	3.966412090359607
1999	4.100500543026964
2000	4.17619194662915
2001	4.764351876356243
2002	4.820199824286522
2003	5.190398263361497
2004	4.417341815815142
2005	5.275970071346791
2006	5.017339254622167
2007	4.871930065920385
2008	3.854011001114249
2009	4.416779024938534
2010	4.6724726063696
2011	4.554968014417175
2012	4.772638582275588
2013	5.281964183389786
2014	5.717815441886042
2015	5.814042908357065