Randomized Block Design(RBD) and Randomized Complete Block Design(RCBD)

Randomized Block Design (RBD)

In RBD, materials are assigned to homogeneous sub-groups which is named a block. It comes in the category of single-factor design. The analysis is easy but becomes complicated when a missing plot technique is required.  In the replication category, RBD differs from treatment to treatment (i.e., 4 to 5 replications are sufficient).

Advantages of Randomized Block Design (RBD):

• The efficiency level is high.
• It reduces experimental errors.
• It increases precision.

Disadvantages of Randomized Block Design (RBD):

• It is not suitable for a larger number of treatments.
• The analysis is easy but becomes complicated when a missing plot technique is required.

Randomized Complete Block Design (RCBD)

It takes advantage of grouping similar experimental units into blocks or replicates. It is used to control variation in an experiment by accounting for spatial effects in the field or greenhouse. e.g. variation in fertility or drainage differences in a field

Key assumption:

It is also known as the two-way ANOVA without interaction. The main assumption in the analysis is that the effect of each level of the treatment factor is the same for each level of the blocking factor.

Randomization Procedure:

• Each replicate is randomized separately.
• Each treatment has the same probability of being assigned to a given experimental unit within a replicate.
• Each treatment must appear at least once per replicate.

For Example: Given four fertilizer rates applied to ‘Amidon’ wheat and three replicates of each treatment.

REP1	REP2	REP3
A	B	A
D	A	B
C	D	C
B	C	D

where, A = 0 KG N/ha, B = 50 KG N/ha, C = 100 KG N/ha, D = 150 KG N/ha

Advantages of Randomized Complete Block Design (RCBD):

• The estimation of missing plots is easy.
• Valid comparisons can be made if the experimental error is heterogeneous.
• Some of the treatments could be replicated more time as compared to others.
• There is no restriction on the number of treatments.

Disadvantages of Randomized Complete Block Design (RCBD):

• In case of missing data, RCBD is not that much efficient.
• In case of large variation between experimental units within a block, a large error term could be its result.