EXAMPLE 3.18 Testing a Breakfast Food

A food company assesses the nutritional quality of a new “instant breakfast” product by feeding it to newly weaned male white rats. The response variable is a rat’s weight gain over a 28-day period. A control group of rats eats a standard diet but otherwise receives exactly the same treatment as the experimental group.

This experiment has one factor (the diet) with two levels. The researchers use30 rats for the experiment and so divide them into two groups of 15. To do this in an unbiased fashion, put the cage numbers of the 30 rats in a hat, mix them up, and draw 15. These rats form the experimental group and the remaining 15 make up the control group. Each group is an SRS of the available rats. Figure 3.5 outlines the design of this experiment.