Year	% of total
1971	66.94632942628007
1972	63.06919292368889
1973	76.49880095923261
1974	75.5730096394145
1975	78.05732484076432
1976	77.03772167985674
1977	77.80762747576907
1978	68.51413311835542
1979	75.26587247249988
1980	74.88829311885613
1981	74.98996225809042
1982	77.82707387536112
1983	81.20815535157078
1984	84.28704159151773
1985	85.84905660377359
1986	81.91768300016838
1987	81.83864753122498
1988	84.640756302521
1989	85.73000455304295
1990	89.70762410747521
1991	88.99666282007298
1992	86.12324538412255
1993	87.10960054590309
1994	90.90720340018076
1995	91.42396535696214
1996	91.86503351051537
1997	92.9125965325014
1998	93.19570092012681
1999	95.58029689608637
2000	96.96215672865394
2001	96.08923098195562
2002	94.2713724600485
2003	92.7702465589623
2004	93.60524329311399
2005	90.91965769731817
2006	90.45525788605059
2007	91.11213514652967
2008	97.57656271850091
2009	96.63007634277454
2010	95.83660644147682
2011	94.74113941979238
2012	94.28809639918828
2013	92.5600341419176
2014	93.17611585927628
2015	93.85674528654863