Suppose researchers want to compare two diets but suspect age strongly influences weight loss. They have older and younger volunteers.
Which design would best account for age differences?
- A
Voluntary-response survey
- Bcheck_circle
Randomized block design with age as the blocking variable
- C
Convenience sample of older volunteers only
- D
Completely randomized design ignoring age
Explanation
Blocking by age separates its effect from the treatment effect, reducing variability and making comparisons more precise.