18. Which instruction would be most appropriate for step 2 of the procedure?
Answer: B
Provide group A participants with a daily magnesium supplement and provide group B participants with a daily supplement that contains only inactive ingredients.
This instruction is appropriate because it establishes a controlled environment where group A receives the active treatment while group B serves as the placebo group, allowing for a clear comparison of the effects of magnesium supplementation.
A) Provide both group A and group B participants with a daily magnesium supplement.
This option is incorrect because it does not create a control group for comparison. Both groups receiving the same treatment would invalidate the experiment's ability to discern the effects of magnesium supplementation.
B) Provide group A participants with a daily magnesium supplement and provide group B participants with a daily supplement that contains only inactive ingredients.
This option is correct as it effectively employs a placebo control for group B, which is essential for evaluating the actual effects of the magnesium supplement administered to group A. This design helps to eliminate psychological effects and allows for a valid assessment of the treatment's efficacy.
C) Provide group A participants with a high-magnesium supplement and group B participants with a low-magnesium supplement...
This choice is inappropriate because it introduces variability in the magnesium levels between the two groups, complicating the results. The goal is to isolate the effect of magnesium supplementation, which cannot be achieved through differing amounts of supplementation.
D) Provide both group A and group B participants with guidelines about which foods they should consume.
While nutritional guidelines can be beneficial, this option does not address the specific supplementation aspect of the study. It fails to create a direct comparison between the active treatment and a control group, which is crucial for the experimental design.
Conclusion
Option B is the only choice that sets up a proper experimental design by incorporating a placebo for group B, allowing for a clear evaluation of the magnesium supplement's effectiveness. Other options either fail to create a valid control group or introduce confounding variables, which would compromise the integrity of the study's results.