Year	Number
1970	12.66977
1973	12.36667
1974	13.36187
1975	13.23397
1978	12.54225
1983	19.86634
1984	16.63321
1985	16.79747
1986	15.45709
1990	18.551
1994	18.40024
1995	18.24207
1996	18.92279
1998	16.40988
1999	16.26507
2000	15.28796
2001	15.64622
2002	15.46392
2003	14.76819
2004	14.93406
2005	15.17113
2006	14.55855
2007	15.8
2008	16.18956
2009	16.17553
2010	16.47759
2011	17.26122
2012	17.75478
2013	18.9254
2014	18.45807
2015	18.10983
2016	18.1118
2017	17.67354
2018	17.99216