Determine whether each study is an observational study or an experiment.

1. Researchers study the effect of vitamin D₃ supplementation among patients with antibody deficiency or frequent respiratory tract infections.

To perform the study, 70 patients receive 4000 IU of vitamin D₃ daily for a year. Another group of 70 patients receive a placebo daily for one year.

2. Researchers conduct a study to determine how confident Americans are in the U.S. economy. To perform the study, researchers call 3040 U.S. adults and ask them to rate current U.S. economic conditions and whether the U.S. economy is getting better or worse.