Insidious Sony 65 Horror 1.5 13.27
Harry Potter and Deathly Hallows P2 Warner Bros 92 Fantasy 125.0 169.19
Bridesmaids Relativity 77 Comedy 32.5 26.25
The Help DreamWorks 91 Drama 25.0 26.04
Horrible Bosses Warner Bros 72 Comedy 35.0 28.30
Transformers: Dark of the Moon DreamWorks 67 Action 195.0 197.85
a). What are the cases in this dataset?
b). Identify each variable as quantitative or categorical:
c). Name a question we might ask about this dataset that is about:
A single variable:
A relationship between two of the variables:
Example 2: Yogurt and Weight Loss
Can eating a yogurt a day cause people to lose weight (as compared to not eating yogurt)? In a study
investigating this:
a). What are the cases?
b). What are the variables and is each quantitative or categorical?
c). What might a dataset look like that might help us answer this question? Make up some data
to show the first couple of rows of such a dataset.
Quick Self-Quiz: Cases and Variables
Give the cases and the variables in each situation below, and identify each variable as categorical or
quantitative:
a). Asking US citizens whether or not they support gun control.
b). Asking college students how many hours of sleep they got last night.
Example 2 Revisited: Yogurt and Weight Loss
Can eating a yogurt a day cause people to lose weight? In a study investigating this:
What is the explanatory variable?
What is the response variable?
Quick Self-Quiz: Explanatory and Response Variables
In each situation, indicate the explanatory variable and the response variable.
a). Does meditation help reduce stress?
b). Is hyperactivity in children affected by sugar consumption?
Section 1.2: Sampling from a Population
Example 1: Driving with a Pet on your Lap
Over 30,000 people participated in an online poll on cnn.com conducted in April 2012 asking “Have you
ever driven with a pet on your lap?” We see that 34% of the participants answered yes and 66%
answered now.
a). What is the sample?
b). Can we conclude that 34% of all drivers have driven with a pet on their lap?
c). Explain why it is not appropriate to generalize these results to all drivers, or even to all
drivers who visit cnn.com. What is the problem with this method of data collection?
d). How might we select a sample of people that would give us results that we can generalize to
a broader population?
e). Is the variable in this study quantitative or categorical?
Quick Self-Quiz: Sampling Bias
You wish to estimate the number of hours a week that students at your university spend studying. For
each sampling method below, indicate whether the results are likely to be representative of the entire
student body or whether the method is likely to give biased results.
a). Ask students you find at the library on a Friday night.
b). Ask students who are at a party on a Tuesday night.
c). Ask a random sample of students.
d). Ask the students in Organic Chemistry.
e). Ask all the students on one of the school’s athletic teams.
f). Send an email out to all students and use all the responses you get.
f). Ask friends that you know, trying to get a reasonably representative group.
Example 2: Public Speeches Against Democracy
How a question is worded can have a dramatic impact on the result. These two questions appear to be
asking the same thing:
 “Do you think the US should allow public speeches against democracy?”
 “Do you think the US should not forbid public speeches against democracy?”
However, 21% said such speeches should be allowed (in answer to the first question) while almost
double that (39%) said such speeches should not be forbidden (in answer to the second question). Why
do you think the results were so different?
Quick Self-Quiz: Wording Bias
A survey is to be conducted using a random sample of citizens in a town, asking them if they support
raising taxes to increase funding for the public school.
a). Write the question in a way that is likely to bias the results toward more yes answers.
b). Write the question in a way that is likely to bias the results toward more no answers.
(In practice, of course, we should try to actually write questions in a way that will NOT bias the results.
The first step is to recognize the effect of leading questions.)
Section 1.3: Experiments and Observational Studies
Example 1: Association or Causation?
For each of the following statements, indicate whether the statement implies causation or just indicates
association without causation.
a). If you study more, your grade will improve in this course.
b). Want to lose weight? Drink tea!
c). Aging of the brain tends to be delayed in people with a college education.
Quick Self-Quiz: Association, Causation, and Confounding Variables
An association is described. In each case, indicate
a). Whether the statement implies causation or just association
b). A possible confounding variable
1. More sales of sunscreen tend to occur when more sunglasses are sold.
2. “Exercise reduces risk of Alzheimers” claims a headline reporting on a study of elderly people that
recorded how much each exercised at age 70 and then whether the person got Alzheimer’s disease.
3. Increased weight helps students run faster.
Example 2: Exercise and Depression
In each case below, we describe a study to determine whether exercise helps increase certain mood
enhancing chemicals in the brain. Indicate whether each describes an experiment or an observational
study.
a). We contact a random sample of 100 people and record how much each person exercises
and also measure the chemicals in the brain for each person.
b). Using a random sample of 100 people, we randomly assign half of them to participate in a
regular exercise program for a six-week period while the other half makes no changes. At the end of the
time period, we measure the brain chemicals.
Example 3: Caffeine and Learning
Does ingesting caffeine help mice learn the way through a maze faster? Describe a well-designed
randomized experiment to test this. Give all details, including the use of placebos and blinding. You
have 20 mice to work with.
Example 4: Is the Dominant Hand Stronger?
Describe a Matched Pairs experiment to see if right hand strength is greater than left-hand strength in
right-handed people. You have a hand-grip to measure strength and 30 right-handed people to use in
your study. Be sure to include how randomization is used in your design.
Quick Self-Quiz: Randomized Experiments
Design a randomized comparative experiment to determine whether taking vitamin B supplements
helps memory. You have 40 people to use in the study and the study will take place over one month.