An agronomist tests a new pesticide on 60 fields. Half the fields are in a high-rainfall region and half in a low-rainfall region. She blocks by rainfall region before randomly assigning treatments.
The primary purpose of blocking by rainfall region is to
- Acheck_circle
Reduce variability due to rainfall, making it easier to detect a pesticide effect
- B
Increase the sample size
- C
Eliminate the need for random assignment
- D
Eliminate placebo effects
Explanation
Blocking controls a source of variability (rainfall) that would otherwise add noise to the comparison, increasing the power to detect a treatment effect.