Chapter 5: Statistical Reasoning
Assignment #2: Unit 5B
Should you Believe a Statistical Study?
Pages 338-345
1. Briefly describe each of the eight guidelines for evaluating statistical
studies. Give an example to which each guideline applies.
1. Identify the Goal, Population and Type of Study
2. Consider the source
3. Look for Bias in the Sample
4. Look for problems in defining or measuring the variables of interest.
5. Watch out for confounding variables
6. Consider the setting and wording in surveys.
7. Check that results are presented fairly.
8. Stand back and consider the conclusions.
2. Describe and contrast selection bias and participation bias in sampling.
Give an example of each.
Selection bias occurs whenever researchers select their sample in a way
that tends to make it unrepresentative of the population. For example, a
pre-election poll that surveys only registered Republicans has selection
bias because it is unlikely to reflect the opinions of all voters.
Participation bias occurs primarily with surveys and polls; it arises whenever
people choose whether to participate. Because people who feel strongly
about an issue are more likely to participate, their opinions may not
represent the larger population that is less emotionally attached to the
issue. (Surveys or polls in which people choose whether to participate are
often called self-selected or voluntary response surveys.)
3. What do we mean by variables of interest in a study?
A variable is any item or quantity that can vary or take on different values.
The variables of interest in a statistical study are the items or quantities that
the study seeks to measure.
4. What are confounding variables, and what problems can they cause?
Variables that are not intended to be part of the study can sometimes
make it difficult to interpret results properly. Such variables are often
called confounding variables, because they confound (confuse) a study’s
results.
It’s not always easy to discover confounding variables. Sometimes they
are discovered years after a study was completed, and sometimes they
are not discovered at all. Fortunately, confounding variables are
sometimes more obvious and can be discovered simply by thinking hard
about factors that may have influenced a study’s results.
Exercises in your textbook: Pages 346 – 347 Problems 15 - 36