year = 2013 
 thc_percent = 12.55%  year = 1995 
 thc_percent = 3.96%  year = 2013 
 thc_percent = 12.55%  year = 2012 
 thc_percent = 12.33%  year = 2011 
 thc_percent = 11.13%  year = 2010 
 thc_percent = 10.36%  year = 2009 
 thc_percent = 9.75%  year = 2008 
 thc_percent = 9.93%  year = 2007 
 thc_percent = 9.58%  year = 2006 
 thc_percent = 8.76%  year = 2005 
 thc_percent = 8.02%  year = 2004 
 thc_percent = 8.14%  year = 2003 
 thc_percent = 7.15%  year = 2002 
 thc_percent = 7.20%  year = 2001 
 thc_percent = 6.11%  year = 2000 
 thc_percent = 5.34%  year = 1999 
 thc_percent = 4.60%  year = 1998 
 thc_percent = 4.91%  year = 1997 
 thc_percent = 5.01%  year = 1996 
 thc_percent = 4.51%  year = 1995 
 thc_percent = 3.96%  year = 2013 
 thc_percent = 12.55%  year = 2012 
 thc_percent = 12.33%  year = 2012 
 thc_percent = 12.33%  year = 2011 
 thc_percent = 11.13%  year = 2011 
 thc_percent = 11.13%  year = 2010 
 thc_percent = 10.36%  year = 2010 
 thc_percent = 10.36%  year = 2009 
 thc_percent = 9.75%  year = 2009 
 thc_percent = 9.75%  year = 2008 
 thc_percent = 9.93%  year = 2008 
 thc_percent = 9.93%  year = 2007 
 thc_percent = 9.58%  year = 2007 
 thc_percent = 9.58%  year = 2006 
 thc_percent = 8.76%  year = 2006 
 thc_percent = 8.76%  year = 2005 
 thc_percent = 8.02%  year = 2005 
 thc_percent = 8.02%  year = 2004 
 thc_percent = 8.14%  year = 2004 
 thc_percent = 8.14%  year = 2003 
 thc_percent = 7.15%  year = 2003 
 thc_percent = 7.15%  year = 2002 
 thc_percent = 7.20%  year = 2002 
 thc_percent = 7.20%  year = 2001 
 thc_percent = 6.11%  year = 2001 
 thc_percent = 6.11%  year = 2000 
 thc_percent = 5.34%  year = 2000 
 thc_percent = 5.34%  year = 1999 
 thc_percent = 4.60%  year = 1999 
 thc_percent = 4.60%  year = 1998 
 thc_percent = 4.91%  year = 1998 
 thc_percent = 4.91%  year = 1997 
 thc_percent = 5.01%  year = 1997 
 thc_percent = 5.01%  year = 1996 
 thc_percent = 4.51%  year = 1996 
 thc_percent = 4.51%  year = 1995 
 thc_percent = 3.96%
The SGPlot Procedure