Year	Percent
1979-01-01	49.3906178831480
1980-01-01	47.9797676828413
1981-01-01	47.8774279386419
1982-01-01	47.8998283399398
1983-01-01	47.7818062781601
1984-01-01	46.9230722245916
1985-01-01	45.6574146777547
1986-01-01	43.1783229478287
1987-01-01	42.3342138685920
1988-01-01	41.1368806770266
1989-01-01	39.4134278736164
1990-01-01	38.1524283051769
1991-01-01	38.3571755291846
1992-01-01	38.2302178161592
1993-01-01	38.3578888403597
1994-01-01	37.2259540984309
1995-01-01	35.9824660513145
1996-01-01	35.7063264858750
1997-01-01	35.9473993231953
1998-01-01	35.8573233575899
1999-01-01	35.8374302402486
2000-01-01	34.7426719562102
2001-01-01	34.0634389004788
2002-01-01	33.8454133487579
2003-01-01	32.9782254750167
2004-01-01	33.2642376960494
2005-01-01	31.8111328751632
2006-01-01	31.1305840329373
2007-01-01	30.5772597131156
2008-01-01	30.0452777302930
2009-01-01	29.8513529091300
2010-01-01	30.0298734733332
2011-01-01	29.5464655314105
2012-01-01	29.6066265032855
2013-01-01	29.5452095129692
2014-01-01	29.4531737933575
2015-01-01	28.7376307946492
2016-01-01	28.3619421790569
2017-01-01	27.6409200954484