Year	Number
1981	10.19864
1991	9.53608
1995	6.87724
1996	6.36477
1997	6.3934
1999	5.04394
2000	5.26776
2001	5.08468
2002	5.72786
2003	5.45143
2004	6.12369
2005	5.92382
2006	6.61727
2007	8.84637
2008	7.28939
2009	7.74376
2010	7.92621
2012	6.38171
2013	6.93395
2014	6.76152
2015	7.08954
2016	7.30595
2017	7.31784
2018	8.32638
2019	7.44479