Hi,
Ionization constant has a lot to do with acid base reactions as it is the propensity for a substance to form ions in water. It is distinct from the ionization energy as it is not dealing with a process where you remove an electron to form an ion from a neutral species.
For example HA --> H+ + A- is governed by an ionization constant.
We have 3 specific ionization constants, those for water (Kw), acids (Ka), and bases (Kb).
An ionization constant can have a value of less than 1, as a value of 1 corresponds to a complete dissociation.
Granted, I'm not actually too familiar with ionization constants so I would call it pretty low yield.
I hope this helps,
Katt