Experimental design - Deciding what
Due: Wednesday, December 3
We talked about four types of
experimental design, and the advantages and disadvantages of
Your assignment is to find recent
articles from the popular press (newspapers, magazines, or online news
sources) that report on research related to physiology. These
are usually listed under Health, but sometimes under Science.
Find two articles, from the last three years (2000-2003), which use
2 of the 4 experimental designs we discussed.
For each one, briefly describe:
- the experimental protocol, that is, what did the experimenters
do? (NOTE: I am asking you to reason backwards from the
results that are reported in the article, and try to deduce what
sort of experimental design was used in the study. If you
can't tell, find a different study. Don't bother going to
the original article for this assignment.)
- which one of the four types of
experimental designs we discussed is used.
- the results
- their conclusion
- one of the reasons why one might question whether the conclusion
is justified, based on the type of experimental design that was
used. (NOTE: This should refer specifically to the
experiment you describe, don't simply repeat the words I
gave you on the handout. See examples below.)
You should write just two (2) brief paragraphs on
each. See examples below.
Sources for news items in physiology:
from Columbia's Libraries, gives links to newspapers and on-line
news sources. Check under Health and Science columns.
- These are sites that specialize in science and health topics:
- Or check magazines and newspapers that you regularly
The articles you choose should report results of recent
research; they should not just be informative articles on
physiological topics, such as a description of how much calcium is
found in different foods or. Look for articles that address
the sort of question we discussed, Does X affect Y?
Many articles report multiple findings and studies. You can
refer just to one of these.
Question: Does sex cause people to look attractive?
What they did: Researchers asked people how often they
had sex, and also rated those people for attractiveness. They
analyzed their data to determine whether there was a correlation
between attractiveness and frequency of having sex.
Critique of design: This study found a correlation
between sex and attractiveness, but that doesn't mean that sex caused
these people to look more attractive. Another possible
explanation is that looking attractive made it more likely that
someone would have sex. Or, gonadal hormones might cause both an
interest in sex, through their effect on the brain, and an increase in
attractiveness, through their effect on secondary sex
Sex makes you look better
Question: Does vitamin C cause people to have fewer colds?
What they did: People were randomly divided into two groups,
and treated in one of two ways, so this is closest to the
interventional design. One group was given Vitamin C to take
when they felt a cold coming on, the other group was given a placebo
that looked like Vitamin C. The researchers compared symptoms
recorded by both groups, and found no difference between them.
They concluded that vitamin C does not prevent colds.
Critique of design: Study of large groups didn't allow
analysis of individual differences. Perhaps vitamin C is helpful in
only certain people - For example, some people might metabolize
vitamin C more rapidly, so that they usually have low levels of the
vitamin, and taking additional vitamin C would then just raise their
blood levels to those of most normal people. If these people are
only 10% of the population, say, then the effect of the vitamin on
them would not be noticeable when a large group of people are
Vitamin C fails to prevent colds