Year	Number
1980	22.9838022165
1981	22.3086104007
1982	21.6334185848
1983	20.958226769
1984	20.2830349531
1985	19.6078431373
1986	19.7851662404
1987	19.9624893436
1988	20.1398124467
1989	20.3171355499
1990	20.494458653
1991	20.5183290708
1992	20.5421994885
1993	20.5660699062
1994	20.589940324
1995	20.6138107417
1996	20.7481515927
1997	20.8824924436
1998	21.0168332946
1999	21.1511741455
2000	21.2855149965
2001	21.4198558475
2002	21.5541966984
2003	21.6885375494
2004	21.8228784004
2005	21.9572192513
2006	22.0915601023
2007	14.5149190111
2008	14.231884058
2009	14.1193520887
2010	14.0903665814
2011	13.1031543052
2012	13.6692242114
2013	13.0451832907
2014	12.42114237
2015	13.9130434783
2016	14.3546462063
2017	14.3546462063
2018	14.3546462063
2019	14.3546462063
2020	14.3546462063