Year	% of total
1971	36.37690561270337
1972	35.93306196432773
1973	35.54691336827753
1974	34.16627081560694
1975	34.472703025714594
1976	33.7781978706578
1977	33.86298791125609
1978	34.918409930849144
1979	34.37008417969866
1980	34.073673301154614
1981	33.347150574176894
1982	33.12019968316696
1983	32.86539511363547
1984	32.63909542827047
1985	32.589952409966905
1986	33.13943010909354
1987	33.37168531502675
1988	33.03639173513833
1989	33.60170730316809
1990	69.45668246779013
1991	69.57870270739429
1992	69.18979292765331
1993	67.85335665946181
1994	67.539015584226
1995	66.73488804073584
1996	67.39404624675032
1997	67.62639447646686
1998	67.67264058278283
1999	68.13513228869587
2000	68.64151923490577
2001	68.88141060947804
2002	69.35252144569986
2003	71.02829809742079
2004	70.7955425842291
2005	71.34726777556247
2006	72.15366003569386
2007	73.27879154944796
2008	72.560200049448
2009	72.1729746579335
2010	72.11756013830316
2011	73.36924234709977
2012	71.90901314482633
2013	71.86407731504
2014	70.62544634070262
2015	69.2577010241485