Year	per 1,000
1990	8
1991	8.5
1992	8.4
1993	8.2
1994	8.1
1995	12.9
1996	12.8
1997	12.7
1998	12.7
1999	12.6
2000	12.5
2001	12.4
2002	12.3
2003	7.3
2004	7.2
2005	7.1
2006	7
2007	7
2008	6.9
2009	6.9
2010	6.7
2011	6.5
2012	6.3
2013	6
2014	5.8
2015	5.7
2016	5.6
2017	5.4
2018	5.3
2019	5.1
2020	5
2021	4.9
2022	5.1