A natural question arises whether the differences between
the smoking and nonsmoking groups are confined
to the low-birth-weight portion of the distribution or whether it is a more generalized phenomenon relating to
the entire birth weight distribution. Figure 4 shows that
the latter is the case. The entire distribution by birth weight
is different for smokers than for nonsmokers for both
white and black mothers. Infants of smoking mothers
weigh less than infants of nonsmoking mothers.