The rate of creationists would also heavily depend on how the question is phrased, because there's not one "creationism" but several, sometimes incompatible, ideologies. Compare these questions:
> Do you believe that a supernatural force created the universe?
> Do believe that God created the earth 6000-10000 years ago?
The first is much broader and would also probably include the origin stories of many non-Abrahamic religions. The second is referring to a specific school of Christian "young earth" creationism.
There's no great way to know the "real" rate of creationists, when apparently people change their stated beliefs for social reasons.