Final answer:
The parameter of interest is the difference in means, as the study compares the average recovery times between the medicine and placebo groups. The use of a placebo helps control for expectancy biases, and the treatment and control groups are independent.
Step-by-step explanation:
The parameter of interest in a study where researchers want to determine whether a medicine is effective for controlling covid-19 symptoms and the length of time to recovery is recorded for each volunteer is the difference in means. This is because two groups (treatment and placebo) are being compared, and the researchers are interested in whether there is a statistical difference in the average recovery times between the two groups. By studying the difference in means, researchers can evaluate if the medicine has a significant effect compared to the placebo. The parameter of interest is the difference in means, as the study compares the average recovery times between the medicine and placebo groups. The use of a placebo helps control for expectancy biases, and the treatment and control groups are independent.
When conducting such an experiment, the use of a placebo is vital to control for the placebo effect. Furthermore, the groups in this study would be independent groups as each volunteer is randomly assigned to only one group—either the treatment group or the control group—and the outcomes are measured independently.