1. Focus Fox
Many utility companies have introduced programs to encourage energy
conservation among their customers. An electric company considers
placing small digital displays in house holds to show current electricity
use and what the cost would be if this use continued for a month. Will
the displays reduce electricity use? One cheaper approach is to give
customers a chart and information about monitoring their electricity use
from their outside meter. Would this method work almost as well?
The company decides to conduct an experiment to compare these two
approaches (display, chart) with a control group of customers who
receive information about energy consumption but no help in
monitoring electricity use.
Outline a completely randomized design involving 60 households in the
same city willing to participate. Write a few sentences describing how
you would implement the design.

2. Good Experiment
Three Principles of Experimental Design
P2
• Control for lurking variables that might affect response variable
Use a comparative design and ensure that the only systematic
difference between groups is the treatment
• Random Assignment – chance accounts for variation among units
Use impersonal chance to assign experimental units to treatments.
This helps create roughly equivalent groups of experimental units
by balancing the effects of lurking variables that aren’t controlled
• Replication – you wouldn’t trust results of 1 student in each class
Use enough experimental units in each group so that any difference
in the effects of the treatments can be distinguished from chance
differences between groups. (use enough subjects)

3. Placebos
Does regularly taking aspirin help protect people against heart attacks?
The Physician’s Health Study was a medical experiment that helped
answer this question. In fact, the Physicians’ Health Study looked at
the effects of two drugs: aspirin and beta-carotene. Researchers
wondered whether beta-carotene would help prevent some forms of
cancer. The subjects in this experiment were 21,996 male physicians.
There were two explanatory variables (factors), each having two levels:
aspirin (yes or no) and beta-carotene (yes or no). Combinations of the
levels of these factors form the four treatments. One-fourth of the
subjects were assigned at random to each treatment.
Odd number days – aspirin or placebo
Even number days – beta-carotene or placebo
After several years, 239 vs. 139 of aspirin group suffered heart attacks

4. Experimental Design
Explain how each of the 3 principles of experimental design were used
in the study.
Pg. 242
The control group – the inactive treatment group (placebo)
* can be used to compare to the effects of aspirin alone, beta-carotene
alone, both, or none.

5. What can go Wrong?
ALL subjects MUST be treated identically
- pill
- cream
Many medical experiments are “placebo-controlled”
The response to an “dummy pill” treatment is called the placebo effect
Strength of placebo effect in medical treatments is hard to pin down
because it depends on exact environment, doctor’s attitude
Pg. 243

6. What can go Wrong?
If some subjects do not take a pill, the effect of aspirin or beta-carotene
would be confounded
If subjects know they are getting “just a placebo” it might weaken the
placebo effect and bias the experiment in favor of other treatments
If the doctors or other medical personnel know what treatment each
subject received, they may change how they interact & diagnose patients
To avoid anyone knowing who has what….
when experiments have human subjects, use a __________________
study.
-

7. What can go Wrong?
It may be impossible to perform a double blind study.
Such experiments can still be conducted as a single-blind study.
- Dieting and exercise
- Pill preventing Alzheimer's
Pg. 244 Check Your Understanding!