Year	Number
1989	13.35017
1990	14.14103
1991	14.70297
1992	12.49158
1993	12.28209
1994	10.80763
1997	10.7853
1999	10.10569
2000	8.94731
2001	14.90522
2002	17.70747
2003	22.57045
2004	20.19121
2005	15.39776
2006	14.82559
2007	13.83652
2008	13.91402
2009	14.76422
2010	14.36452
2011	16.58641
2012	14.05
2013	13.08337
2014	13.33981
2015	15.43954
2016	15.866
2017	14.45916
2018	14.37169