In the randomized block design the researcher is interested to isolate one of the major extraneous factors influencing the experiment such as store size. This major extraneous factor is considered in addition to the influence of the treatment on the test unit.

In the previous example twelve stores were taken to test the influence of different prices on the sales. But no allowance were made for variation in the store size. In the randomized block design an extraneous factor which is major in influencing the experiment is taken into account, after separating it form the total environment. Thus, in this case, we get a truer premature of the treatment influence on the test unit. It is necessary that the additional variable separated out must be identified and measured during the time of experiment.

Suppose, in the previous example, we want to measure the effect of different prices on sales, keeping the store size in mind. We may increase the number of stores form twelve to thirty-size and divide them into three categories accordant store sizes. These categories are called blocks. The prices are distributed randomly within each of the three blocks. Suppose, we use monthly sales turnover as a criterion to divide stores into three block a follows: Block I constitutes stores having sales turnover in excess of Rs. 1000: Block II constitutes stores having sales turnover ranging from Rs 600 to Rs. 1000; and Block III constitutes tares having sales turnover less than Rs. 600. This is along with the sales of number of packets of soap in each block.

On applying variance analysis to these results of it might be found that sales of packets at the stores size does not influence the sales turnover to a significant extent. Thus, the size may not influence the treatment in a significant manner.

Randomised Block Design

Sr.   Block-store size depending---No. of packets of soap No.    upon sales turnover-------------sold at various prices -------------------------------------------Rs. 6.00 Rs. 6.50  Rs7.00

1. Rs. 1,000 and above--------------- 500-------550---------450  (per month) 2. Rs. 600 to Rs. 1.000-----------------600------300-------- 250 (per month) 3. Below Rs. 600 (per  month)-------400------350---------150

Total:----------------------------------1.500--------1,200-------850

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