Year	% of total
1971	38.85150291610588
1972	50.53366174055829
1973	54.953670705630785
1974	67.11212516297263
1975	66.00550964187329
1976	67.74498229043684
1977	70.16824849007766
1978	76.05839416058394
1979	83.15445636957536
1980	84.14993682437175
1981	83.46843527388847
1982	82.29033631332481
1983	85.9757291055001
1984	85.44088714004651
1985	85.40003258921297
1986	88.84523534396426
1987	87.43122150605251
1988	90.76328225690963
1989	91.17723831897678
1990	93.73447590660705
1991	93.99250504468147
1992	94.67898939079078
1993	94.95209642526012
1994	95.3980787607504
1995	95.69870656860259
1996	95.74416577902586
1997	95.80406568358376
1998	95.62806293525922
1999	96.44544977178172
2000	96.74563198488903
2001	96.83004694835681
2002	97.63454861111111
2003	96.78062967096142
2004	96.99839999999999
2005	96.24944714727997
2006	97.25202975075229
2007	97.25776965265082
2008	97.32826324684363
2009	97.6286330225189
2010	97.51169808020292
2011	96.93503045447447
2012	97.07127550220395
2013	97.94289530806478
2014	98.61150026462438
2015	98.35751039274398