As an epidemiologist you are going to investigate the effect of a drug suspected of causing malformations in newborn infants when the drug in question is taken by pregnant women during the course of their pregnancies. As your sample you will use the next 200 single births occurring in a given hospital. For each birth a medication history will be taken from the new mother and from her doctor; in addition, you will review medical records to verify use of the drug. [N.B.: These mothers are considered to have been followed prospectively during the entire course of their pregnancies, because a complete and accurate record of drug use was maintained during pregnancy.]
The resultant data are:
Forty mothers have taken the suspected drug during their pregnancies. Of these mothers, 35 have delivered malformed infants. In addition, 10 other infants are born with malfunctions.
The number of individuals who both did not take the drug and did not give birth to infants who were malformed was: