Question

For the experiment described below, do the following:

A drug made by Company A for preventing coccidiosis in chickens is being compared to two different generic competitors made by Companies B & C. Each company's drug can be given at equivalent high and low doses. There are 56 cages which were placed in 8 different rooms with 7 cages per room. Six 1-day-old chicks were placed into each cage. One cage in each room was assigned at random to get no drug in its feed. The remaining six cages in each room received medicated feed where each combination of drug (A, Br C) & dose level (high or low) was randomly assigned to one cage in each room. After two days, each chick was infected with an organism known to cause coccidiosis. At the end of the study, each bird was euthanized and given an intestinal lesion score of 0, 1,2, 3 or 4 where each score corresponds to degree of intestinal damage observed (0 no damage, 1 minor damage..., & 4 - most severe damage including death).

1/ Describe the treatment structure of the experiment including the treatment factor(s) and their corresponding levels

2/ Identify the experimental unit(s) and the observational unit. Specify the total number of (each size of) experimental units used in the experiment

3/ Identify the design structure and any factors associated with the design e structure (e.g. blocking factors).

4/ Classify the response on the OU as nominal, ordinal, interval or ratio

Answer 1

1) There are 3 treatments and each of the treatments take two levels. In our experiment the 3 drugs namely A,B and C correspond to the 3 treatments and each of the drugs take two levels namely high and low. There are 56 cages and 8 rooms ( each room has 7 cages). There are 6 treatment combinations applied

A at high level is applied to chickens in one of the cages in each room

A at low level is applied to chickens in one of the cages in each room

Similarly for the treatments B and C at high and low levels each are applied to one of the cages in each room

And the chickens in one cage is each room are not given any drug

2) Experimental units refer to the chickens to which the experiment is applied and the observational units refer to the chickens on which the response is measured. Here the drugs are applied to 288 chickens ( Since there are 6 chickens in each cage and the treatment is applied to the chickens in 6 cages in each of the 8 rooms=> 8*6*6). And all the chickens are observed , so the number of observational units is 336 (8 rooms with 6 cages and 6 chickens in each cage => 8*6*6)

3) Here there are 6 treatment combinations are applied to the chickens there is no blocking here only replication is applied

4) The response variable is ordinal in nature