Year	Percent
1968-01-01	30.8252795609166
1969-01-01	31.1512806795548
1970-01-01	31.1578773564679
1971-01-01	31.3214667094603
1972-01-01	31.6914113489674
1973-01-01	31.3556235390355
1974-01-01	32.1919240153643
1975-01-01	32.6587331911139
1976-01-01	32.5589434035542
1977-01-01	32.1966550957912
1978-01-01	31.7392601719553
1979-01-01	31.4911980284994
1980-01-01	31.5013710024428
1981-01-01	31.3348251644338
1982-01-01	31.0485029797895
1983-01-01	30.3973583008632
1984-01-01	30.5599257277428
1985-01-01	30.7897303625120
1986-01-01	30.7974988043339
1987-01-01	30.8483736919560
1988-01-01	30.7383383457363
1989-01-01	30.2633954729472
1990-01-01	29.6625663109984
1991-01-01	28.9927912240392
1992-01-01	28.6520256904012
1993-01-01	28.5789005458648
1994-01-01	28.5172880211287
1995-01-01	28.4121118142520
1996-01-01	27.9224532898123
1997-01-01	27.3589034185056
1998-01-01	27.3297969339863
1999-01-01	27.4348631869451
2000-01-01	27.4349548381660
2001-01-01	27.3447932948792
2002-01-01	27.6197169246403
2003-01-01	27.5691431710514
2004-01-01	27.6191204679574
2005-01-01	27.2647128524201
2006-01-01	26.8191628543580
2007-01-01	26.2635333267698
2008-01-01	26.0653990652407
2009-01-01	25.9064032671389
2010-01-01	25.7948628225569
2011-01-01	25.6023336255465
2012-01-01	26.0130290510252
2013-01-01	25.0723094104874
2014-01-01	24.4035068803298
2015-01-01	23.9161738425575
2016-01-01	23.0361662075995
2017-01-01	22.3729716700845