A factor is a variable that is controlled and varied during the course of an experiment. In a chemistry experiment, temperature and pressure may be the factors that are deliberately changed over the course of the experiment. In the clinical trial, treatment can be a factor. A study of experimental therapy vs. placebo can be thought of as having a treatment factor with 2 levels, 0 or the study dosage. A study with two different treatments has the possibility of a two-way design, varying the levels of treatment A and treatment B.
Factorial clinical trials are experiments that test the effect of more than one treatment using a type of design that permits an assessment of potential interactions among the treatments.
In a factorial design, there are two or more factors with multiple levels that are crossed, e.g., three dose levels of drug A and two levels of drug B can be crossed to yield a total of six treatment combinations:
low dose of A with low dose of B
low dose of A with high dose of B
mid dose of A with low dose of B
mid dose of A with high dose of B
high dose of A with low dose of B
high dose of A with high dose of B
Factorial designs offer certain advantages over conventional designs. There are a number of ways that you could look at these groups. This lesson will consider these alternatives...
- identify the conditions that would allow a factorial design to be useful
- recognize the difference between qualitative and quantitative interactions
- recognize the situation for which a ‘min’ test is the appropriate analysis
Piantadosi Steven. (2005) Reporting and Authorship. Factorial Designs. In: Piantadosi Steven. Clinical Trials: A Methodologic Perspective. 2nd ed. Hobaken, NJ: John Wiley and Sons, Inc.