1985, Cambridge, Massachusetts
1985, Washington, District of Columbia
1982, Denver, Colorado
1981, Houston, Texas
1978, Washington, District of Columbia
1977, Boston, Massachusetts
1971, Boston, Massachusetts
1968, Boston, Massachusetts
1967, Cambridge, Massachusetts
1967, Boulder, Colorado
1964, Boston, Massachusetts
1958, Denver, Colorado
1956, Denver, Colorado
1942, Des Moines, Iowa