Researchers examine the association between the fluoridation of water and the prevention of tooth decay by comparing the prevalence of tooth decay in countries that have fluoridated water with the...

Researchers examine the association between the fluoridation of water and the prevention of tooth decay by comparing the prevalence of tooth decay in countries that have fluoridated water with the prevalence in countries that do not.

a. Is this a randomized experiment or an observational study?

b. Assume that tooth decay was seen to be less common in countries with fluoridated water. Could this result be due to confounding?