environment in which the experiment was conducted. The randomization controlled for
unknown influences that might be present in the various tank locations.
You will need to recognize paired data, as distinct from two independent sets of data, later on
when we study inference. Even though two sets of data are generated in a matched-pairs study, it is
the differences between the matched values that form the one-sample data used for statistical
analysis.Exam Tip: You need to be clear on the distinction between the purposes for blocking and randomizing.
If you are asked to describe an experiment involving blocking, be sure to remember to randomize
treatments within blocks.Rapid Review
You are doing a research project on attitudes toward fast food and decide to use as your sample the
first 25 people to enter the door at the local FatBurgers restaurant. Which of the following is (are)
true of this sample?
a. It is a systematic sample.
b. It is a convenience sample.
c. It is a random sample.
d. It is a simple random sample.
e. It is a self-selected sample.
Answer : Only (b) is correct. (a), (c), and (d) are all probability samples, which rely on some random
process to select the sample, and there is nothing random about the selection process in this situation.
(e) is incorrect because, although the sample members voluntarily entered Fat Burgers, they haven’t
volunteered to respond to a survey.
- How does an experiment differ from an observational study ?
Answer : In an experiment, the researcher imposes some treatment on the subjects (or experimental
units) in order to observe a response. In an observational study, the researcher simply observes,
compares, and measures, but does not impose a treatment.
What are the three key components of an experiment? Explain each.
Answer : The three components are randomization, control, and replication. You randomize to be sure
that the response does not systematically favor one outcome over another. The idea is to equalize
groups as much as possible so that differences in response are attributable to the treatment variable
alone. Control is designed to hold confounding variables constant (such as the placebo effect).
Replication ensures that the experiment is conducted on sufficient numbers of subjects to minimize the
effects of chance variation.
Your local pro football team has just suffered a humiliating defeat at the hands of its archrival. A
local radio sports talk show conducts a call-in poll on whether or not the coach should be fired. What