Year	Number
1979	30.22683
1980	30.46719
1981	30.72808
1982	31.36634
1983	31.71011
1984	31.96146
1985	31.75881
1986	31.23183
1987	30.90279
1988	30.78263
1989	30.04102
1990	28.97223
1991	28.26215
1992	27.33967
1993	25.98158
1994	24.69212
1995	23.55602
1996	22.02782
1997	20.12975
1998	19.0342
1999	15.46428
2000	11.28127
2001	13.01731
2002	12.23878
2003	12.05037
2004	11.42004
2005	10.83433
2006	11.68272
2007	13.28005
2008	14.22399
2009	15.38208
2010	15.6878
2011	17.2876
2012	17.97429
2013	18.31585
2014	18.80971
2015	19.45791
2016	19.3476