Year	Number
1981	14.98855
1986	13.76491
1989	11.26217
1990	10.88961
1991	10.56415
1992	10.29524
1993	9.84891
1994	9.54567
1995	9.75573
1999	11.09398
2000	11.50156
2003	12.91747
2004	12.97119
2005	13.30873
2006	13.03556
2007	13.06257
2008	12.57795
2009	12.27106
2010	13.00627
2011	13.27681
2012	12.84043
2013	11.68829
2014	10.90033
2015	10.69989
2016	10.43487
2017	10.32977