Maternal years of education is self-reported by the participants. Participants are asked about the number of years of education completed by their mother:

What was the highest grade or year of regular school your mother completed? [Number of years]

If the exact number is not known, participants are asked the following supplemental question to help estimate a value for years of education:

Would you say that she had no schooling, a few years, finished grammar school, had any high school, or any college?

Response choices for supplemental question: