Year	Percent
1979-01-01	31.2668731019642
1980-01-01	30.5390128234689
1981-01-01	30.5783304562161
1982-01-01	30.8341515673746
1983-01-01	31.1316295532422
1984-01-01	30.9039817719174
1985-01-01	30.4823721365666
1986-01-01	29.0687384033164
1987-01-01	28.8695751762314
1988-01-01	28.2807571300900
1989-01-01	27.2689473425956
1990-01-01	26.4912776717381
1991-01-01	27.0186045746987
1992-01-01	27.1765475210010
1993-01-01	27.4141067481580
1994-01-01	26.8082397640482
1995-01-01	26.0365334552657
1996-01-01	25.9694626956972
1997-01-01	26.4071392536970
1998-01-01	26.4844258597571
1999-01-01	26.6631051550318
2000-01-01	26.2071616561920
2001-01-01	25.9445717183034
2002-01-01	25.8521360787536
2003-01-01	25.5107050442798
2004-01-01	25.6315936838061
2005-01-01	24.6033622120211
2006-01-01	24.1982991865051
2007-01-01	23.8085725305481
2008-01-01	23.4967570066893
2009-01-01	23.6138650820166
2010-01-01	23.5654157915017
2011-01-01	23.3565362881411
2012-01-01	23.5719670069518
2013-01-01	23.5974764918064
2014-01-01	23.6922955649330
2015-01-01	23.0576853183334
2016-01-01	23.0531905042557
2017-01-01	22.5560495218119