Year	Number
1981	9.73132
1986	9.25504
1989	9.26483
1990	9.12652
1991	8.84968
1992	8.64891
1993	8.0569
1994	8.06525
1995	7.47518
1999	7.81012
2000	8.65662
2001	9.36639
2002	9.3365
2003	9.99382
2004	9.92732
2005	9.92012
2006	9.9486
2007	9.87078
2008	9.78732
2009	9.78279
2010	9.60995
2011	9.67628
2012	9.71192
2016	13.38868
2017	13.32609
2018	11.8808