Year	Percent of Total
1960-01-01	36.4609795065671
1961-01-01	36.3683025129848
1962-01-01	36.2812672652010
1963-01-01	36.1173836935871
1964-01-01	35.7972298098717
1965-01-01	35.3037228496787
1966-01-01	34.8740967913956
1967-01-01	34.2996580461319
1968-01-01	33.6724080699296
1969-01-01	33.1458848168143
1970-01-01	32.8082812387046
1971-01-01	32.5836628451020
1972-01-01	32.5354771810218
1973-01-01	32.5941422994275
1974-01-01	32.6415322066587
1975-01-01	32.6170896318585
1976-01-01	32.8291221076512
1977-01-01	32.9313633102217
1978-01-01	32.9656407254663
1979-01-01	32.9940059085627
1980-01-01	33.0326835470283
1981-01-01	33.0283453273615
1982-01-01	33.0471972595621
1983-01-01	33.0521606542379
1984-01-01	32.9934289975673
1985-01-01	32.8547141940052
1986-01-01	32.5871438191772
1987-01-01	32.2913472127251
1988-01-01	31.9642714005298
1989-01-01	31.6130650916726
1990-01-01	31.2521678267294
1991-01-01	30.8405973641443
1992-01-01	30.3724709691989
1993-01-01	29.8819102076496
1994-01-01	29.4172245373274
1995-01-01	29.0015653243075
1996-01-01	28.7345458163215
1997-01-01	28.5334537029277
1998-01-01	28.3822271868674
1999-01-01	28.2416659170334
2000-01-01	28.0885724875747
2001-01-01	28.0579098234285
2002-01-01	27.9900341144859
2003-01-01	27.9114055726111
2004-01-01	27.8624393572436
2005-01-01	27.8582213761383
2006-01-01	27.6756566153152
2007-01-01	27.5553488278031
2008-01-01	27.4684286239628
2009-01-01	27.3780922811901
2010-01-01	27.2732855110027
2011-01-01	27.4264101425145
2012-01-01	27.5706072329186
2013-01-01	27.6988226088257
2014-01-01	27.7993141953948
2015-01-01	27.8592089549481
2016-01-01	27.9056029985005
2017-01-01	27.8622783921784