Year	Number
1980	32.01254
1981	32.24301
1982	32.36023
1983	32.87682
1984	33.17535
1985	33.46186
1986	33.07539
1987	33.02343
1988	32.96629
1989	32.63813
1990	32.2719
1991	32.00675
1992	31.61545
1993	31.31298
1994	31.03362
1995	30.62418
1996	30.35154
1997	30.57536
1998	30.12122
1999	28.40179
2000	28.24137
2001	29.76802
2002	28.60836
2003	29.71576
2004	30.66322
2005	32.38584
2006	32.19908
2007	29.81311
2008	31.53978
2009	31.84185
2010	29.03604
2011	28.45063
2012	29.05419
2013	28.77699
2014	27.98925
2015	27.87061
2016	28.32147
2017	31.76163
2018	28.72051