Year	Number
1976	21.49553
1977	21.21221
1978	21.24195
1979	20.30558
1980	20.59869
1981	20.76468
1982	21.93353
1983	21.5633
1984	22.52136
1985	22.44197
1986	22.30721
1987	22.5137
1988	22.45668
1989	22.33904
1990	22.47776
1991	21.8401
1992	22.12613
1993	22.07824
1994	21.60679
1995	21.88215
1996	21.21252
1997	21.00629
1998	20.74316
1999	20.36682
2000	19.04476
2001	19.73398
2002	20.75247
2003	20.0749
2004	20.69337
2005	20.38526
2006	20.85605
2007	20.61487
2008	21.80764
2009	22.60049
2010	22.31552
2011	20.78537
2012	19.55656
2013	19.8897
2014	20.88724
2015	21.36064
2016	22.28557
2017	22.25088
2018	22.35409