Three diets for hamsters (labeled \"I\",\"II\",\"III\") were tested for differen

Question

Three diets for hamsters (labeled "I","II","III") were tested for differences in weight gain (measured as grams of increase) after a specified period of time. Six inbred laboratory lines (labeled "A","B","C", "D", "E", "F") were used to represent the responses of different genotypes to the various diets. The lines were treated as blocks and all three diets were assigned randomly within each block. The data consisted of a total of 18 observations. Both one-way ANOVA and two-way ANOVA models were fit to the data. Below are two different models of the data.

1. What kind of design model corresponds to the one-way ANOVA? Explain this design.

Explanation / Answer

The design is known as CRD (Completely Randomised Design))

A completely randomized design is probably the simplest experimental design, in terms of data analysis and convenience. With this design, subjects are randomly assigned to treatments.

A completely randomized design layout for a hypothetical medical experiment is shown in the table to the right. In this design, the experimenter randomly assigned subjects to one of two treatment conditions. They received a placebo or they received a cold vaccine. The same number of subjects (500) are assigned to each treatment condition (although this is not required). The dependent variable is the number of colds reported in each treatment condition. If the vaccine is effective, subjects in the "vaccine" condition should report significantly fewer colds than subjects in the "placebo" condition.

A completely randomized design relies on randomization to control for the effects of extraneous variables. The experimenter assumes that, on averge, extraneous factors will affect treatment conditions equally; so any significant differences between conditions can fairly be attributed to the independent variable.

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