Experimental Design: Understanding Local Control

The question asks for the experimental design principle where an extraneous factor is deliberately varied, measured, and its effect removed from the experimental error.

Key Principles Explained

• Principle of Local Control: This involves managing variability. Known sources of extraneous variation (factors other than the treatment) are deliberately controlled. This is often done by making the factor vary across experimental units (e.g., different locations in a field) and accounting for its effect, thereby reducing the experimental error associated with treatment comparisons.
• Principle of Randomisation: Uses random assignment of treatments to reduce bias.
• Principle of Replication: Repeats experiments or treatments to increase reliability.
• Principle of Observation: Refers to the act of watching or noting, not a specific experimental design control technique.

Identifying the Correct Principle

The deliberate variation, measurement, and subsequent elimination of an extraneous factor's influence directly corresponds to the Principle of Local Control. This technique isolates the effect of the factor of interest by accounting for known sources of noise.