Year	Number
1998	17.39354
1999	17.67762
2000	15.89496
2001	16.44165
2002	14.97061
2003	14.621
2004	14.45852
2005	13.85873
2006	11.33879
2007	11.45076
2008	9.3755
2009	8.38793
2010	7.97018
2011	8.36528
2012	8.26996
2013	6.45115
2014	5.79197
2015	6.53521
2016	6.3232
2017	5.93281