When I was doing the survey I found the 'Highest Education Credential Earning' question difficult because the credentials listed don't match those in my home country, Australia. For example, we have a system of "technical certificates" that fall in between High School and Bachelor's degrees. (I think I chose '2 year degree' as the closest approximation, even though mine only took 1 year to complete.) And I know that doing a Bachelors in some areas is the functional equivalent of doing a Masters in others.

Would a question asking for how many years of post-schooling study one has completed be more or less useful? The wording could be tricky, since then there is ambiguity about whether to list time spent if one is part way through a qualification. If the majority of respondents are from places that match the listed options then mucking about with the question may not be of much value either.