Year	Number
1974	16.13863
1975	14.57405
1976	17.49323
1977	17.78609
1978	15.59666
1980	15.62311
1981	17.13415
1982	16.32124
1983	15.19083
1985	13.75657
1987	12.2738
1988	13.0594
1989	13.22567
1990	12.57055
1994	13.26778
1998	14.2328
2000	16.33087
2003	17.13753
2004	17.13724
2008	28.07678
2010	19.76935
2012	19.35122
2013	21.40783
2014	19.93308
2015	19.97027
2016	21.47298
2017	24.64953
2018	21.45735