Several creationist writers have discussed the growth of populations. Usually they have taken the growth to be geometric or exponential. Then, from known facts about present populations, they have tried to calculate back to the time of the Flood, or of creation. Here I shall comment mostly on Rodabaugh's work, since it appeared recently in the Quarterly, and had some refinements which were not found in other treatments. If the constraints in the treatment are arranged to make the formula fit the present populations, and some for ancient times, say in Jacob's day, the formulae give populations in intermediate times, say David's time or the beginning of the Christian era, which are too low by as much as five orders of magnitude. A more elaborate formula can fit the known figures for the Jewish population, for instance. But the result is of little use in proving the youth of the earth, or in finding the time of the Flood. It is recommended, then, that because of the discrepancies which may be introduced, that these arguments about populations not be used in popular public lectures.