Year	% of total
1971	79.21791113847544
1972	79.08091413698612
1973	78.75129727876735
1974	76.98014634001836
1975	74.33107288418802
1976	74.66038248306506
1977	74.34558105582431
1978	73.67666977432455
1979	74.35713516414948
1980	73.93812572652169
1981	73.99479201067768
1982	70.22013962615202
1983	68.43689792670726
1984	68.27018630986038
1985	66.81436033707509
1986	66.70517493614027
1987	65.9129898290639
1988	69.30602800938844
1989	73.80845139940476
1990	72.15647686849252
1991	68.03674235506925
1992	66.35600412655944
1993	68.07402800420205
1994	69.82379098513
1995	70.00781440778779
1996	72.39165887642538
1997	74.65556429878895
1998	75.52716035803182
1999	77.16421959661803
2000	74.511496953145
2001	73.10697124996149
2002	73.20071836367903
2003	74.56344116489754
2004	75.18353617600222
2005	74.24470723386366
2006	74.0091485100545
2007	76.02644650186484
2008	75.18426694537938
2009	73.47402667786712
2010	77.60667222819674
2011	76.67911718387683
2012	70.03944214917182
2013	68.64980209194164
2014	73.25054382893518
2015	74.64721226256785