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 conduc 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?

(a)  It is an experiment.

(b) Group III has been tested to compare the effect of tea

Step-by-step explanation:

24 volunteers are randomly selected to one of the three groups.

Group I drinks two cups of hot black tea without milk

Group II drinks two cups of hot black tea with milk

Group III drinks two cups of hot water but no tea.

At the end of the month, the researchers measured the change in each of the participant's heart health.

The average change of health status of three Groups can be measured and let it be X1', X2' and X3'. We can set up the hypothesis of no difference of heart health i.e H0 : µ1 = µ2 = µ3 against the alternative hypothesis that they are not equal. As the sample size is less than 30, we can use t-statistic.

Under the above logic, (a) it is an experiment.

(b) Group III has been tested to compare the effect of tea or to have comparison between GroupI and Group III.