Year	Number
1970	37.3272
1971	37.22037
1972	37.15193
1973	37.16118
1974	37.0412
1975	37.18545
1976	37.43335
1977	37.64338
1978	36.46222
1979	36.41639
1980	37.26752
1981	37.34219
1982	37.35694
1983	36.99026
1984	36.88924
1985	36.97005
1986	36.69128
1987	37.09195
1988	36.67471
1989	35.39976
1990	36.18189
1991	36.14438
1992	36.09621
1993	36.6168
1994	37.79622
1995	38.17957
1996	38.15706
1997	40.67384
1998	41.15776
1999	41.08075
2000	42.28521
2001	42.44817
2002	43.13351
2003	42.42988
2004	42.63169
2005	42.76424
2006	43.41366
2007	44.30129
2008	43.81452
2009	43.17023
2010	41.61294
2011	40.82243
2012	42.22734
2013	38.79557
2014	37.98205
2015	37.50596
2016	37.50599
2017	37.36845
2018	37.36194