Question

Randomized Complete Block Design (RCBD) is to conduct research in a manner that is effective, cost efficient, and detects statistically significant treatment effects. RCBDs are used when similar experiment units (eu’s) are grouped into blocks and there are enough eu’s in each block for at least one replicate of each treatment. Search for a video, news item, or article that gives a better understanding of Randomized Complete Block Designs and give your feedback.

Answer 1

Randomized Complete Block Design commonly known as RCBD, is an experimental design in which the experimental units are arranged in blocks or homogenous units. Each block/unit contains a complete set of treatments which are assigned randomly to the blocks or units. The design is said to be complete because in RCBD the number of experimental units and the number of treatments are equal. One of the main assumptions of RCBD is that there is no interaction between the treatments and the block effects hence variation is controlled. RCBD is preferred over all other designs because it controls the effects of the treatments on the response variables.

Layout of Randomised Complete Block Design

Suppose that there are four treatments and three blocks then the experimental layout would look like this:

Block 1	Block 2	Block 3
A	B	C
B	C	D
C	D	A
D	A	B

As seen in the above layout each treatment occurs only once in each block.

Advantages of RCBD

• It is generally more precise than completely randomized design(CRD)
• There is no restriction on the number of treatments or the number of replicates
• In some cases certain treatments will be replicated more than others
• Missing plots are easily estimated

Disadvantages of RCBD

• In RCBD the number of degrees of freedom for error is less than that for the CRD(this is the problem with small number of treatments).
• Large variation between the experimental units within the block may result in a large error term
• If missing data exists, a RCBD experiment is less efficient than a CRD

The general model of RCBD is given as

As with all the other designs

where =overall mean, =effect of ith treatment, =effect of jth block and =unexplained error, i is the number of treatments and j is the number of blocks.