Year Measure 1800 1623 1820 1623 1850 2062 1870 2225 1890 2877 1900 3305 1910 3805 1913 4005 1920 3695 1921 3984 1922 3834 1923 4110 1924 4497 1925 4981 1926 4922 1927 5259 1928 5690 1929 5815 1930 5592 1931 5368 1932 5122 1933 4877 1934 4669 1935 4606 1936 4967 1937 5507 1948 5903 1949 6230 1950 6691 1951 6735 1952 6876 1953 6774 1954 6979 1955 7496 1956 7856 1957 8256 1958 8811 1959 9136 1960 9764 1961 10060 1962 10140 1963 9881 1964 10270 1965 10570 1966 10970 1967 11400 1968 11890 1969 12140 1970 12360 1971 12730 1972 13110 1973 13460 1974 13840 1975 14140 1976 14260 1977 14800 1978 14880 1979 14920 1980 15260 1981 15120 1982 15380 1983 15570 1984 15900 1985 15990 1986 16260 1987 16310 1988 16640 1989 16760 1990 16270 1991 14380 1992 14300 1993 14300 1994 14620 1995 15490 1996 16140 1997 16050 1998 15960 1999 16210 2000 16820 2001 17260 2002 17600 2003 18240 2004 19060 2005 20280 2006 21640 2007 22800 2008 23290 2009 22060 2010 22530 2011 22900 2012 22570 2013 22590 2014 22910 2015 23500 2016 24120 2017 24800 2018 25520