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Part V: Statistical Studies and the Hunt for a Meaningful Relationship
aware of some of the limitations of experiments such as cost, time, as well as
ethical issues, and realize that the number of subjects for experiments is often
smaller than the number of participants in a survey.
If the results are important to you, ask for a copy of the research report
and look to see what type of analysis was done on the data. Also look at the
sample of subjects to see whether this sample truly represents the popula-
tion about which the researchers are drawing conclusions.
Defining sample size
When asking questions about sample size, be specific about what you mean
by the term. For example, you can ask how many subjects were selected to
participate and also ask for the number who actually completed the experi-
ment; these two numbers can be very different. Make sure the researchers
can explain any situations in which the research subjects decided to drop
out or were unable (for some reason) to finish the experiment.
For example, an article in The New York Times titled “Marijuana Is Called an
Effective Relief in Cancer Therapy” says in the opening paragraph that mari-
juana is “far more effective” than any other drug in relieving the side effects
of chemotherapy. When you get into the details, you find out that the results
are based on only 29 patients (15 on the treatment, 14 on a placebo). Then
you find out that only 12 of the 15 patients in the treatment group actually
completed the study. What happened to the other three subjects?
Sometimes researchers draw their conclusions based on only those subjects
who completed the study. This can be misleading, because the data don’t
include information about those who dropped out (and why), which may be
leading to biased data. For a discussion of the sample size you need to achieve
a certain level of accuracy, see Chapter 13.
Accuracy isn’t the only issue in terms of having “good” data. You still need to
worry about eliminating bias by selecting a random sample (see Chapter 16
for more on how random samples are taken).
Choosing the subjects
The first step in carrying out an experiment is selecting the subjects (par-
ticipants). Although researchers would like their subjects to be selected
randomly from their respective populations, in most cases, this just isn’t
appropriate. For example, suppose a group of eye researchers wants to test
out a new laser surgery on nearsighted people. They need a random sample
of subjects, so they randomly select various eye doctors from across the
country and randomly select nearsighted patients from these doctors’ files.
They call up each person selected and say, “We’re experimenting with a

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