To the Editor:—Thank you for letting me see Dr. Knobloch's letter concerning our article, "Premature and Full-Term Infants." I should like to comment upon some of the points which she raises.
"Comparable" white and nonwhite groups, comparable in education, socioeconomic status, etc.—that is, comparable in everything but race—would be most difficult to find, and they would be essential only if white and nonwhite groups were to be compared with each other. In our article, with the exception noted below, white study has been compared with white control and nonwhite study with nonwhite control.
Bias in the selection of the Negro mother for admission to the hospital, especially bias in regard to prematurity, the entity which is being studied, does not seem likely. The nonwhite prematurity rate (including stillbirths) was 14.0%, which approximates the rates in other series.
Cases and controls were not initially matched for race, nor does such