Year Percent 1990-01-01 0.2239690000000000 1991-01-01 0.7402280000000000 1992-01-01 1.4521600000000001 1993-01-01 2.4382700000000000 1994-01-01 5.0266400000000000 1995-01-01 9.0625400000000000 1996-01-01 11.9579000000000000 1997-01-01 14.0875000000000000 1998-01-01 16.8013000000000000 1999-01-01 17.3630000000000000 2000-01-01 17.1377000000000000 2001-01-01 17.4913000000000000 2002-01-01 18.1032000000000000 2003-01-01 18.7362000000000000 2004-01-01 18.0632000000000000 2005-01-01 17.6735000000000000 2006-01-01 17.1239000000000000 2007-01-01 15.7308000000000000 2008-01-01 14.5065000000000000 2009-01-01 14.1236000000000000 2010-01-01 14.3407000000000000 2011-01-01 15.2842000000000000