Compare populations A double-blind study using random assignment was done of pregnant women in Denmark. Women were given fish oil or a placebo during pregnancy. Their children were followed during the first 5 years of life to see if they developed asthma. The results are summarized in the table. (Bisgaard et al., "Fish Oil- Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring," New England Journal of Medicine, vol. 375: 2530-2539.) Developed asthma Yes No Fish oil 58 288 Placebo 83 266 The researchers want to find out if there is a significant difference in the population proportions of children who develop asthma in the two groups.