Year	Number
1976	36.11604
1977	35.57718
1978	34.14532
1979	34.61545
1980	36.43103
1981	38.64422
1985	35.29414
1986	34.46203
1987	35.00456
1988	34.96487
1989	34.49841
1990	34.18834
1991	35.11028
1992	35.09961
1993	35.5758
1994	35.19029
1995	34.86643
1996	34.22652
1997	33.48732
1998	32.15427
1999	30.43485
2000	29.52151
2001	28.03482
2002	26.32905
2003	24.65381
2004	23.02694
2005	21.55565
2006	20.6947
2007	20.43643
2008	19.92674
2009	19.5222
2010	19.90175
2011	19.63155
2012	19.39912
2013	18.88349
2014	19.21383
2015	19.2242
2016	19.62995
2017	19.64643
2018	20.27696