Year	% of total
1971	97.30232558139534
1972	96.23318385650225
1973	95.52772808586762
1974	95.42902967121091
1975	95.22058823529412
1976	94.7209653092006
1977	94.23076923076923
1978	94.16604338070307
1979	94.3042537851478
1980	93.94356503785272
1981	94.81403876375066
1982	94.87895716945997
1983	96.53419593345656
1984	98.28519855595668
1985	97.82875870544858
1986	98.10330912025827
1987	97.72727272727273
1988	98.05566145634769
1989	98.41152567417805
1990	98.47979236188358
1991	98.56088560885608
1992	98.72122762148338
1993	98.9406779661017
1994	98.82352941176471
1995	98.85098743267504
1996	98.86246122026887
1997	98.84910485933503
1998	98.35858585858585
1999	98.75592417061611
2000	98.9080459770115
2001	98.10787913018922
2002	96.42424242424242
2003	95.76547231270358
2004	95.37712895377129
2005	94.2057942057942
2006	76.22405013709361
2007	73.37402250619874
2008	74.49392712550608
2009	69.44492477952619
2010	72.21562976775725
2011	74.26110454315149
2012	74.01058201058201
2013	74.1016333938294
2014	74.15474642392718
2015	74.99260136134951