Year	Number
1970	56500000
1971	64300000
1972	71500000
1973	77700000
1974	79200000
1975	82700000
1976	92200000
1977	107000000
1978	118000000
1979	126000000
1980	120000000
1981	117000000
1982	111000000
1983	109000000
1984	109000000
1985	102000000
1986	116000000
1987	120000000
1988	122000000
1989	122000000
1990	121000000
1991	124000000
1992	127000000
1993	130000000
1994	133000000
1995	138000000
1996	145000000
1997	151000000
1998	158000000
1999	165000000
2000	172000000
2001	178000000
2002	184000000
2003	187000000
2004	189000000
2005	189000000
2006	187000000
2007	184000000
2008	182000000
2009	181000000
2010	179000000
2011	177000000
2012	174000000
2013	175000000
2014	173000000
2015	172000000
2016	171000000
2017	171000000
2018	172000000