Assignment #4

Experimental design - Deciding what to measure

Due:  Wednesday, December 3

Write concisely. 

We talked about four types of experimental design, and the advantages and disadvantages of each.  

  • Correlative
  • Retrospective
  • Prospective
  • Experimental

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:

  1. 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.)
  2. which one of the four types of experimental designs we discussed is used.  
  3. the results
  4. their conclusion
  5. 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:

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 characteristics.   

Sex makes you look better
Health Central


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 studied.  

Vitamin C fails to prevent colds
Health Central