Year per 1,000 people 1960 2.75537443161011 1970 3.81369996070862 1981 4.82550001144409 1990 4.1729998589 1997 4.3000001907 2000 4.12 2001 3.85 2002 3.9 2003 3.9 2004 3.9 2005 3.4 2006 3.7 2007 3.7 2008 3.7 2009 3.7 2010 3.7 2011 3.7 2012 3.7 2013 3.7 2014 3.7 2015 3.7 2016 3.7 2017 3.2