Year	% of total
1971	35.21469855628695
1972	35.08213565633587
1973	34.801118729689954
1974	33.690104433591436
1975	33.936602507158675
1976	33.42916074608378
1977	33.57357376959763
1978	34.07547726983556
1979	33.94187148259832
1980	33.932824536880325
1981	33.54309655106497
1982	33.86079350761405
1983	34.03959894642912
1984	34.01698454211847
1985	34.383447456011105
1986	34.845874644377474
1987	35.690735723752894
1988	35.280349295176194
1989	35.78825768683366
1990	68.64834444665668
1991	68.80858983680673
1992	68.6423024329321
1993	67.65889825545624
1994	67.38179726009383
1995	67.31714512602889
1996	67.84355736952037
1997	68.33655908323205
1998	68.28948159570608
1999	68.94856411030207
2000	69.5692381178038
2001	69.75451448710068
2002	70.3952717861854
2003	71.45173414771838
2004	71.24427938810209
2005	71.45064554195972
2006	71.99735088494877
2007	72.98460396843042
2008	72.80592399116858
2009	72.67677930233789
2010	72.45144652727579
2011	73.27412261735375
2012	72.35181611250934
2013	72.11861004465523
2014	71.3937924725047
2015	70.67390814974098