Year	Number
1992	16.03614
1993	16.19042
1994	16.45705
1995	16.95173
1996	16.91941
1997	16.73566
1998	16.55083
1999	16.28747
2000	16.01508
2001	16.5215
2002	15.24984
2003	15.25176
2004	14.88757
2005	14.8281
2006	14.51739
2007	14.47279
2008	14.2112
2009	14.09545
2010	13.78122
2011	14.91214
2012	15.29527
2013	15.34068
2014	15.44892
2015	15.38726
2016	15.32718
2017	15.20269
2018	15.19855