Year	% of total
1971	41.111353830702264
1972	40.89961306317838
1973	40.67861133637541
1974	39.73503060828134
1975	39.789634731933596
1976	39.502636351900904
1977	39.35559614899958
1978	39.65390627313409
1979	39.40491714503754
1980	39.1237897441461
1981	38.546457938702204
1982	38.65320310558979
1983	38.644545027331965
1984	38.45007735958203
1985	38.59117023390896
1986	38.96180172530791
1987	39.454365636700786
1988	38.90674631882129
1989	39.45044961433475
1990	70.71693554986686
1991	70.46444077006953
1992	70.24600888653761
1993	69.24163058075348
1994	68.92435242619416
1995	68.71086046617778
1996	69.16680880420023
1997	69.30839241578977
1998	69.29803401565984
1999	69.99332052448216
2000	70.51410338767371
2001	70.73510403141022
2002	71.44290887273395
2003	72.72645861841575
2004	72.30459715592251
2005	72.34119214447428
2006	72.8865215767519
2007	73.85731416120626
2008	73.56523969145135
2009	73.35432860648089
2010	73.27537067688782
2011	74.13986719655796
2012	73.24280219165928
2013	72.93928469066367
2014	72.06723561418684
2015	71.34837045804922