Year	Number
1981	5.92415
1986	9.0309
1989	8.18398
1990	8.2735
1991	7.74867
1992	6.99565
1993	6.61059
1994	6.19919
1995	6.00585
1996	5.95422
1997	6.36762
1999	7.07495
2000	9.42071
2002	10.64216
2003	12.39506
2004	13.6158
2005	14.85179
2006	14.86086
2007	12.64745
2008	13.71146
2009	14.27611
2010	14.26559
2011	13.43652
2012	12.57387
2013	11.71386
2014	10.54873
2015	10.75556
2016	10.49584
2017	10.3608