| Year | Ann Avg |
|---|---|
| 1948 | 3.8 |
| 1949 | 5.9 |
| 1950 | 5.3 |
| 1951 | 3.3 |
| 1952 | 3.0 |
| 1953 | 2.9 |
| 1954 | 5.5 |
| 1955 | 4.4 |
| 1956 | 4.1 |
| 1957 | 4.3 |
| 1958 | 6.8 |
| 1959 | 5.5 |
| 1960 | 5.5 |
| 1961 | 6.7 |
| 1962 | 5.5 |
| 1963 | 5.7 |
| 1964 | 5.2 |
| 1965 | 4.5 |
| 1966 | 3.8 |
| 1967 | 3.8 |
| 1968 | 3.6 |
| 1969 | 3.5 |
| 1970 | 4.9 |
| 1971 | 5.9 |
| 1972 | 5.6 |
| 1973 | 4.9 |
| 1974 | 5.6 |
| 1975 | 8.5 |
| 1976 | 7.7 |
| 1977 | 7.1 |
| 1978 | 6.1 |
| 1979 | 5.8 |
| 1980 | 7.1 |
| 1981 | 7.6 |
| 1982 | 9.7 |
| 1983 | 9.6 |
| 1984 | 7.5 |
| 1985 | 7.2 |
| 1986 | 7.0 |
| 1987 | 6.2 |
| 1988 | 5.5 |
| 1989 | 5.3 |
| 1990 | 5.6 |
| 1991 | 6.8 |
| 1992 | 7.5 |
| 1993 | 6.9 |
| 1994 | 6.1 |
| 1995 | 5.6 |
| 1996 | 5.4 |
| 1997 | 4.9 |
| 1998 | 4.5 |
| 1999 | 4.2 |
| 2000 | 4.0 |
| 2001 | 4.7 |
| 2002 | 5.8 |