Explain what is wrong with each of the following randomization procedures, and d

Question

Explain what is wrong with each of the following randomization procedures, and describe how you would do the randomization correctly.

(c) An experiment will assign 40 rats to four different treatment conditions. The rats arrive from the supplier in batches of 10, and the treatment lasts two weeks. The first batch of 10 rats is randomly assigned to one of the four treatments, and data for these rats are collected. After a one-week break, another batch of 10 rats arrives and is assigned to one of the three remaining treatments. The process continues until the last batch of rats is given the treatment that has not been assigned to the three previous batches.

Explanation / Answer

(c) If we are administering only one treatment condition to a whole batch of rats, then our obtained results are not compensated for the batch effects of the rats. We can randomly assign the 4 treatments to (3,3,3,1) to each batch of rats and for each batch select a different treatment received by the single rat. Our procedure would look like

In this way we can adjust for the batch effect and any biases towards a single treatment.

Batch 1 A (3) B(3) C(3) D(1) Batch 2 A(3) B(3) D(3) C(1) Batch 3 A(3) C(3) D(3) B(1) Batch 4 B(3) C(3) D(3) A(1)

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