Year	per 1,000
1990	3.9
1991	4.1
1992	75.4
1993	83.5
1994	31.2
1995	10.6
1996	3.1
1997	2.8
1998	2.6
1999	2.4
2000	2.2
2001	2.1
2002	2.1
2003	2.1
2004	2.1
2005	2.2
2006	2.2
2007	2.2
2008	2.2
2009	2.2
2010	2.2
2011	2.2
2012	2.2
2013	2.2
2014	2.3
2015	2.3
2016	2.3
2017	2.3
2018	2.3
2019	2.3
2020	2.2
2021	2.2
2022	2.1