Q. I can’t find any reference in CMOS 16 to how odds should be punctuated.
A. Odds are ratios. Ratios may be expressed in numerals with a colon and no spaces (CMOS 6.60) or with numbers spelled out or not according to the guidelines at 9.2:
The odds are 451:1.
The odds are 3:2.
The odds are 451 to 1.
The odds are three to two.