Year	Number
1981	11.49424
1999	9.0733
2001	7.53579
2002	7.3906
2003	7.80251
2004	8.50679
2005	9.04021
2006	9.18398
2007	9.20215
2008	9.1243
2009	9.20378
2010	8.94176
2011	9.30599
2013	8.20747
2014	7.74275
2016	7.67398