Scientists want to test a new pair of running shoes. A speed test is performed with two separate groups of participants. The treatment group will wear the new pair of running shoes, while the control group will not. It is believed that age and height may affect speed. Which of the following would be most effective in controlling the confounding variables, such as age and height, in this study? a. A completely randomized design experiment
b. A longitudinal observational study
c. A retrospective observational study
d. A matched-pair design experiment

a. A completely randomized design experiment

Step-by-step Explanation:

An experiment that is completely randomised is practically an effective way of controlling and reducing the influence of the confounding variables in a research study, especially when you have a sample that is large enough.

Randomisation will ensure that both the group that will wear the new shoe (treatment group) and the group that will not wear the new shoe (control group) will have averagely the same values for age and height. This will eliminate the chances of these confounding variables of correlating with the independent variable in the study, as there would be no difference, in terms of characteristics, between both groups.