Download 5.2 Experiment Design Date Comparative Experiments often have a

5.2 Experiment Design
Date _________________________
Comparative Experiments often have a very simple design:
Units
Treatments
Observe Response
Completely Randomized Experimental Design
Example 1: Consider the following question: Will taking antioxidants help prevent colon cancer?
Subjects will be divided into 4 groups and followed four 4 years.
1. Daily beta carotene
2. Daily vitamins C and E
3. Daily beta carotene, vitamins C and E
4. Daily placebo
Some vocabulary we need:
Experimental units
Subjects
Treatment
Explanatory variables
Levels
Placebo
Control group
Placebo effect
Diagram a completely randomized experiment to examine whether or not antioxidants help prevent colon
cancer.

Advantages of the completely randomized experiment

Disadvantages of the completely randomized experiment
A few more vocabulary words we need to know:
Blind
Double Blind
Statistically significant
Matched Pairs Experimental Design: Subjects are matched to reduce the effects of lurking variables
as two treatments are compared
Example 2: Consider the question of whether or not talking on a hands free cell phone distracts drivers.
In general we will: 1. Match subjects (or use each subject as his or her own pair)
2. Randomly assign treatments (or the order of the treatments)
3. Describe the design in a paragraph
Design a matched pairs experiment to examine whether or not talking on a hands free device distracts
drivers.

Advantages of the matched pairs experiment

Disadvantages of the matched pairs experiment
Randomized Block Design: A block is a group of subjects or units that is similar in a way that is
expected to affect the response to the treatment. The purpose of blocking is to create homogenous
groups to reduce or control lurking variables.
We will: 1. Divide subjects into blocks
2. Randomizations of subjects to treatments occurs within the blocks
3. Comparisons are made within the blocks
Example 3: Researchers were interested in whether adding calcium to the diet would help reduce blood
pressure. They were also concerned that patients being treated for high blood pressure and patients without
high blood pressure would react differently.
Diagram a randomized block design experiment to see if calcium reduces blood pressure.

Advantages of randomized block design experiment

Disadvantages of the randomized block design experiment
The three basic principles of experimental design are listed below. What does each of them mean and why
are they important, or essential for good experimental design?
1. Control
2. Randomization
3. Replication