Year	% of total
1971	10.372836106876536
1972	10.087931410197557
1973	9.371982838980554
1974	9.437887284901421
1975	9.143811737541316
1976	8.654878798761919
1977	8.566909855400986
1978	8.364195565796956
1979	8.788878619282805
1980	8.917670718411525
1981	8.693365885103905
1982	8.376932959204266
1983	7.935551340300508
1984	8.459004600998812
1985	8.101716690435998
1986	7.599015991387445
1987	7.972626391253323
1988	7.749600529693926
1989	8.767283282520076
1990	14.722525643528284
1991	14.616590048326394
1992	14.599304202142022
1993	14.703463962306579
1994	14.910198930147194
1995	15.169258040069586
1996	15.184065001388852
1997	15.981884165001025
1998	16.53373059627644
1999	17.438804487068523
2000	17.736694174685585
2001	18.57940803826749
2002	19.12243085669294
2003	19.405618443797373
2004	19.93364822321346
2005	20.138893373156982
2006	20.491084603717475
2007	21.183732221411976
2008	21.583429886241678
2009	21.90185396832796
2010	22.377921751810817
2011	21.959523350991553
2012	22.377892958261558
2013	21.478682663352174
2014	21.58553197916411
2015	22.776074279964824