A swim instructor would like to test the effect of a new swim technique versus the standard technique for a group of 25 competitive swimmers.The swim instructor divides the students by class (junior or senior), and then randomly allocates half of the 14 juniors and 5 of the 11 seniors to receive instruction on the new technique.During swim practice, the instructor times the juniors as they race against each other to see if those who learned the new technique outperform their peers. The instructor does the same for the seniors.At the end of practice, the instructor compares the average swim time for both juniors and seniors among those who did and did not use the new technique.What type of experimental design did the instructor use?
Answer
A
matched pairs experimental design
B
completely randomized experimental design
C
randomized block experimental design
D
none (observational study only)
Explanation
The instructor first groups swimmers by class—junior or senior—then randomly assigns swimmers to the new or standard technique within each group. This is a randomized block experimental design: class is the blocking variable, and the technique is the treatment being tested. It is not a matched pairs design because swimmers are not arranged into individual pairs.
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