Statistics: Blocking Introduction

Objectives

• Students will recognize that blocking can reduce variation.
• Students will describe random allocation of treatments as occurring within each block.
• Students will recognize that the experimental units within each block are as similar as possible and as different as possible from the experimental units in the other blocks based on a variable that has the potential to affect the outcome of an experiment.

Vocabulary

• experiment
• experimental units
• random allocation
• randomized block design
• simple random sample
• treatments

About the Lesson

This lesson involves investigating the effectiveness of two mosquito sprays in a large tract of land by using two different experimental designs - one randomized design and one randomized block designs.
As a result, students will:

• Select a random sample to be used in an experiment.
• Randomly allocate treatments and observe the mean number of mosquitoes in the plots after the sprays have been applied.
• Examine a sampling from a population and observe a pattern in a measured variable regardless of assigned treatments (i.e., more mosquitoes closer to the swamp).
• Compare the variability in a completely randomized design with a randomized block design.