Year	Number
1980	11.63107
1989	11.09904
1990	10.07843
1999	7.27091
2000	7.62922
2001	7.25404
2002	7.95262
2003	8.32081
2004	8.67364
2005	9.25901
2006	9.46229
2007	9.49101
2008	9.78508
2009	10.06521
2010	9.83875
2011	9.47919
2012	9.39831
2013	8.6052
2014	8.9872
2015	8.7287
2016	8.55367
2017	8.39484
2018	6.2709