The pattern of relative disadvantage is even more pronounced for the population of mothers who smoke.
These mothers are much more likely to be African-American (though less likely to be Hispanic), have a year less education, are much less likely to be married, and live in the poorest census tracts compared to non-smoking mothers who live within 10 km of a monitor.
In contrast, mothers with more than one birth in the sample look quite similar to mothers observed to have had only one birth.