Randomized Block Design
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A randomized block design (RBD) is a type of experimental layout in which the various treatments to be tested
are randomly assigned to the experimental units or participants within each block of the subject population.
in essence, separates subjects with similar features into blocks and randomly assesses the impact of each
treatment on each subject in the block
Reduce the differences between components within a blocked group in comparison to the variations within the
components of the overall sample.
Purpose
1. The most precise relationship between dependent and independent variables requires a thorough
understanding of the project and the ability to foresee probable causes of variation.
2. To obtain the most precise variable association, there are advantages in using block randomization to
Benefits of Block Randomization:
· reduce bias
· reduce errors
· minimizes variability among treatment circumstances.
· aids in preventing inaccurate interpretation of results.
· assists in comparing how the independent and dependent variables are affected.
· produces a better estimate of treatment effects.
· enhances the reliability of the statistical analysis.
Limitations:
1. We Can't block on too many variables—As the number of blocking variables and blocks created increases, the
number of participants in each block would be very low.
2. Difficulty in choosing the number of blocks—It will be important to pick a blocking variable with the right number of
categories. NOT TOO MUCH OR TOO FEW CATEGORIES
3. Difficulty in detecting the blocking variable—When the blocking variable is known but uncontrollable, and when it is
unknown.
Example