CHAPTER 4 Designing Studies - Mrs. Robinson's Class€¦ · · 2017-10-31The Practice of Statistics, 5th Edition Starnes, Tabor, Yates, Moore Bedford Freeman Worth Publishers CHAPTER

The Practice of Statistics, 5th Edition

Starnes, Tabor, Yates, Moore

Bedford Freeman Worth Publishers

CHAPTER 4Designing Studies

4.3

Using Studies Wisely

Learning Objectives

After this section, you should be able to:

The Practice of Statistics, 5th Edition 2

DESCRIBE the scope of inference that is appropriate

EVALUATE whether a statistical study has been carried out in an

ethical manner.*



The Idea of a Sample Survey

What type of inference can be made from a particular study? The

answer depends on the design of the study.

Well-designed experiments randomly assign individuals to treatment

groups. However, most experiments don’t select experimental units at

random from the larger population. That limits such experiments to

inference about cause and effect.

Observational studies don’t randomly assign individuals to groups,

which rules out inference about cause and effect. Observational studies

that use random sampling can make inferences about the population.


Silence is golden?Many students insist that they study better when listening to music. A teacher

doubts this claim and suspects that listening to music actually hurts academic

performance. Here are four possible study designs to address this question at

your school. In each case, the response variable will be the students’ GPA at

the end of the semester.

For each design, suppose that the mean GPA for students who listen to music

while studying was significantly lower than the mean GPA of students who

didn’t listen to music while studying.

Problem: What can we conclude for each design?

1. Get all the students in your AP® Statistics class to participate in a study.

Ask them whether or not they study with music on and divide them into

two groups based on their answer to this question.

With no random selection, the results of the study should be applied only to the AP®

Statistics students in the study. With no random assignment, we should not conclude

anything about cause and effect. All we can conclude is that the students in the AP®

Statistics class who listen to music while studying have lower GPAs than those who

do not listen to music while studying. We don’t know why and we can’t apply these

results to any larger group of students.











2. Select a random sample of students from your school to participate in

a study. Then divide them into two groups as in Design 1.

With random selection, the results of the study can be applied to the entire

population—in this case, all the students at this school. With no random assignment,

however, we should not conclude anything about cause and effect. All we can

conclude is that students at this school who listen to music while studying have lower

GPAs than those who do not listen to music while studying. We don’t know why their

GPAs are lower, however.











3. Get all the students in your AP® Statistics class to participate in a study.

Randomly assign half of the students to listen to music while studying for

the entire semester and have the remaining half abstain from listening to

music while studying.

With no random selection, the results of the study should be applied only to the AP®

Statistics students in the study. With random assignment, however, we can conclude

that there is a cause-and-effect relationship between listening to music while

studying and GPA, but only for the AP® Statistics students who took part in the study.











4. Select a random sample of students from your school to participate in a

study. Randomly assign half of the students to listen to music while

studying for the entire semester and have the remaining half abstain from

listening to music while studying.

With random selection, the results of the study can be applied to the entire

population—in this case, all the students at this school. With random assignment, we

can conclude that there is a cause-and-effect relationship between listening to music

while studying and GPA for all the students at the school.


The Challenges of Establishing Causation

A well-designed experiment tells us that changes in the explanatory

variable cause changes in the response variable.

Lack of realism can limit our ability to apply the conclusions of an

experiment to the settings of greatest interest.

In some cases it isn’t practical or ethical to do an experiment. Consider

these questions:

•Does texting while driving increase the risk of having an accident?

•Does going to church regularly help people live longer?

•Does smoking cause lung cancer?

It is sometimes possible to build a strong case for causation in the

absence of experiments by considering data from observational

studies.


Do calories matter?

Does including the number of calories on a menu encourage diners to

make healthier choices?

Two AP® Statistics students designed a study to find out. They

randomly assigned students to look at one of two different menus and

indicate what they would order if they dined at the restaurant. One of

the menus listed the number of calories for each item and the other

menu did not.

Result: no significant difference in the average number of calories

ordered. The two students speculated that there wasn’t a difference

because the students weren’t actually at the restaurant and didn’t get to

eat the food they “ordered.” In other words, the experiment suffered

from a lack of realism.


Do tanning beds cause skin cancer?

Doctors have noticed that people who frequently visit tanning salons

are at a much greater risk for skin cancer.

But are the tanning beds the cause?

Could the association be due to another variable, such as sun

exposure? After all, people who like to tan indoors also probably like to

tan outdoors.

An experiment would help to settle this question, but forcing people to

use tanning beds to see if they get skin cancer is unethical.


The Challenges of Establishing Causation

When we can’t do an experiment, we can use the following criteria for

establishing causation.

The example in your book on page 269 about smoking and lung cancer

is an excellent example of this use of establishing causation.

The association is strong.

The association is consistent.

Larger values of the explanatory variable are associated with

stronger responses.

The alleged cause precedes the effect in time.

The alleged cause is plausible.


Data Ethics*

Complex issues of data ethics arise when we collect data from people.

Here are some basic standards of data ethics that must be obeyed by

all studies that gather data from human subjects, both observational

studies and experiments.

All planned studies must be reviewed in advance by an institutional

review board charged with protecting the safety and well-being of the

subjects.

All individuals who are subjects in a study must give their informed

consent before data are collected.

All individual data must be kept confidential. Only statistical

summaries for groups of subjects may be made public.

Basic Data Ethics

Section Summary

In this section, we learned how to…


DESCRIBE the scope of inference that is appropriate

EVALUATE whether a statistical study has been carried out in an

ethical manner.*



PAGE 273

100, 102, 104

Homework

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CHAPTER 4 Designing Studies - Mrs. Robinson's Class€¦ · · 2017-10-31The Practice of Statistics, 5th Edition Starnes, Tabor, Yates, Moore Bedford Freeman Worth Publishers CHAPTER