Researchers investigated the possible beneficial effect on heart health of drinking black tea and whether adding milk to the tea reduces any possible benefit. Twenty-four volunteers were randomly assigned to one of three groups. Every day for a month, participants in group 1 drank two cups of hot black tea without milk, participants in group 2 drank two cups of hot black tea with milk, and participants in group 3 drank two cups of hot water but no tea. At the end of the month, the researchers measured the change in each of the participants’ heart health.

Did the researchers conduct 1 drank two cups of hot black tea participants in group 3 drank two d the change in each of the participants' heart bealth. t an experiment or an observational study?

The researchers conducted an experiment by randomly assigning participants to three groups and monitoring the effects of black tea consumption, with and without milk, on heart health. Controlled experiments allow for stronger inferences of causality compared to observational studies, which can be affected by confounding factors.

The researchers conducted an experiment by setting up distinct conditions for different groups and measuring the effects of those conditions on heart health. Group 1 consumed two cups of hot black tea without milk daily, Group 2 consumed two cups of hot black tea with milk, and Group 3 drank just hot water. The design included random assignment to groups, consistent dosages of the test substance (in this case, tea), and a control condition. This structure allows researchers to infer cause-and-effect relationships more reliably than in observational studies, where confounding factors could skew results.

Observational studies, such as those examining the health effects of coffee, often find correlations. However, without controlled experimental conditions, it's difficult to conclude causality. For instance, other lifestyle factors could be the actual cause of observed health outcomes rather than coffee consumption itself. Furthermore, in observational studies where variables like lifestyle habits are controlled, no correlation is often found, as in the case of the LibreTexts study on coffee consumption and health.