Year	% of total
1971	99.33108704630345
1972	99.36350194018699
1973	99.48787549655643
1974	99.30030103570745
1975	99.40830209338613
1976	99.43398408081609
1977	99.56141385704011
1978	97.79865977486914
1979	97.44106220518766
1980	97.39015432117692
1981	97.5618546577621
1982	97.31503876466331
1983	94.4903243930075
1984	93.54388925695885
1985	91.19473875269378
1986	87.3144613263913
1987	83.71814547824907
1988	85.4666551955285
1989	83.84311535614162
1990	83.780131574621
1991	84.33809459996561
1992	85.82812264438925
1993	86.92320800625208
1994	87.73615025249478
1995	87.0837253333585
1996	87.0688775734844
1997	87.564120738008
1998	84.15197467532653
1999	83.59460003337546
2000	83.96860009408262
2001	83.75121502401397
2002	83.43111204115063
2003	82.21699509190489
2004	82.4851138419253
2005	80.61091993650365
2006	80.5471681682196
2007	81.81923465111839
2008	81.16937769722166
2009	81.65563804843761
2010	82.86953009216111
2011	82.74552314062554
2012	83.22136322292252
2013	84.16471753399024
2014	82.3950038022924
2015	81.02847580714447