Year	Number
1987	31.51618
1988	31.00598
1989	30.4187
1990	30.99225
1991	30.78964
1992	30.69045
1993	30.53526
1994	30.33326
1995	30.18862
1996	29.98214
1997	29.74472
1998	29.61811
1999	29.332
2000	30.26417
2001	30.05877
2002	29.8274
2003	30.27429
2004	30.46917
2005	30.76868
2006	30.38994
2007	29.17266
2008	31.60862
2009	32.14661
2010	30.10848
2011	30.38057
2012	31.64431
2013	30.78212
2014	29.45542
2015	29.49748
2016	29.5885
2017	33.90469
2018	29.74233