3.7 How to Experiment Well

Describe how to randomly assign treatments using slips of paper or technology.

Using slips of paper: Label each paper with a letter or number. Shuffle and hand out one to each volunteer. For example, if you have 100 volunteers and you want two groups, label 50 with A and 50 with B.

Using a number generator: Label the volunteers with a number, then randomly generate the amount needed (ignore repeats). For example, if you have 100 volunteers and you want two groups, after you assign each of them a number, generate 50 numbers. The remaining 50 will be in the other group.

Explain the purpose of random assignment in an experiment.

Random assignment should distribute the volunteers in roughly equal numbers to each group. In fact, the random assignment should create two groups that are roughly equivalent with respect to every variable that might affect the response.

The purpose of random assignment is to create groups that are roughly equivalent at the beginning of an experiment.

Identify other sources of variability in an experiment and explain the benefits of keeping these variables the same for all experimental units.

Although random assignment should create groups of experimental units that are roughly equivalent at the beginning of an experiment, there are other variables that might have an impact on the response variable.

Depending on the experiment, some factors to consider might be temperature, amount, time, etc.

One reason to keep other variables the same for each subject is to prevent confounding.

The second reason we keep other variables the same is to reduce the variability in the response variable, making it easier to determine if one treatment is more effective than another.