Year	Number
1976	29.92557
1977	30.24474
1978	31.93331
1992	29.4319
1993	28.7496
1994	27.96393
1995	27.82225
1996	27.79433
2001	26.2789
2002	24.85287
2003	23.42655
2004	22.49661
2005	21.924
2006	23.47558
2007	23.8074
2008	23.49545
2009	23.14925
2010	23.91437
2011	24.06572
2012	24.4299
2013	23.74954
2014	23.65918
2015	23.15243
2016	23.16642
2017	22.93257
2018	21.73735