Your statistic is for the fraction of children living in single-mother households. dinoleif's statistic is for the fraction of babies born to single mothers. So your statistic doesn't count babies who are adopted to two-parent households or whose father later marries the mother (probably plus other factors I'm not considering). I'd say your statistic is more directly relevant to "is there a male adult living in the same house", but dinoleif's for "is the child being raised with a legally committed biological father".