Year	Number
1983	12.34701
1984	12.59626
1985	12.65927
1986	12.96757
1987	13.24489
1988	12.18466
1989	13.1498
1990	14.13916
1991	14.59615
1992	15.47566
1993	16.60083
1994	17.10658
1995	22.05856
1996	20.40373
1997	21.04721
1999	22.57864
2000	21.45123
2001	21.43441
2002	22.79198
2003	22.64284
2004	20.09694
2005	18.70358
2006	18.60183
2007	18.18529
2008	17.36226
2009	17.50795
2010	17.66389
2011	17.83285
2012	17.85441
2013	16.42327
2014	15.52415
2015	15.68994
2016	15.78774
2017	15.55958