Research Methodology Chapter 2.6

Randomized block design is a commonly used experimental design in biological research. It is a variation of the completely randomized design that allows for the control of extraneous variables that may influence the outcome of the experiment. In this section, we will explore the concept of randomized block design, its advantages, and how to implement it in biological research.

Definition and Purpose

Randomized block design is a type of experimental design where the subjects or experimental units are divided into homogeneous groups called blocks. Each block consists of similar individuals or units that share common characteristics. The purpose of using randomized block design is to reduce the variability within each block and increase the precision of the experiment by accounting for the variability between blocks.

Advantages of Randomized Block Design

There are several advantages to using randomized block design in biological research:

• Control of extraneous variables: By grouping similar individuals or units into blocks, randomized block design allows for the control of extraneous variables that may affect the outcome of the experiment. This control increases the internal validity of the study.

• Increased precision: Randomized block design increases the precision of the experiment by reducing the variability within each block. This increased precision enhances the ability to detect treatment effects and make accurate conclusions.

• Efficiency: Randomized block design is more efficient than a completely randomized design when there are significant differences between the blocks. By accounting for the variability between blocks, the experiment can be conducted with fewer subjects or units, saving time and resources.

Implementation of Randomized Block Design

• Identify the blocks: Determine the characteristics or factors that will be used to create the blocks. These factors should be relevant to the research question and should result in homogeneous groups.
• Assign treatments randomly: Randomly assign the treatments to the subjects or units within each block. This random assignment ensures that any differences observed between the treatments are not due to systematic biases.
• Replicate the experiment: Repeat the experiment within each block to increase the precision of the results. The number of replications will depend on the research question and available resources.
• Collect and analyze data: Collect data on the outcome variable of interest for each treatment within each block. Analyze the data using appropriate statistical methods, such as analysis of variance (ANOVA), to determine the significance of the treatment effects.

Example of Randomized Block Design in Biological Research

To illustrate the application of randomized block design in biological research, consider a study investigating the effect of different fertilizers on plant growth. The researcher divides the experimental units, which are individual plants, into blocks based on their initial size. Within each block, the researcher randomly assigns the different fertilizers. The experiment is replicated multiple times to increase the precision of the results. Finally, the researcher measures the plant growth and analyzes the data using ANOVA to determine if there are significant differences between the fertilizers.

Randomized block design is a valuable experimental design in biological research that allows for the control of extraneous variables and increases the precision of the experiment. By grouping similar individuals or units into blocks, randomized block design reduces variability within each block and accounts for variability between blocks. This design is particularly useful when there are significant differences between the blocks. By following the steps outlined in this section, researchers can effectively implement randomized block design in their biological research studies.