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dCHAPTER 2
THE SCIENTIFIC METHOD
CHAPTER OUTLINE AND OBJECTIVES
I. Scientific and Everyday Approaches to Knowledge
The scientific method is empirical and requires systematic, controlled observation.
Scientists gain the greatest control when they conduct an experiment; in an experiment, researchers
manipulate independent variables to determine their effect on behavior.
Dependent variables are measures of behavior used to assess the effects of independent variables.
Scientific reporting is unbiased and objective; clear communication of constructs occurs when
operational definitions are used.
Scientific instruments are accurate and precise; physical and psychological measurement should be
valid and reliable.
A hypothesis is a tentative explanation for a phenomenon; testable hypotheses have clearly defined
concepts (operational definitions), are not circular, and refer to concepts that can be observed.
A. General Approach and Attitude
B. Observation
C. Concepts
D. Reporting
E. Instruments
F. Measurement
G. Hypotheses
II. Goals of the Scientific Method
The scientific method is intended to meet four goals: description, prediction, explanation, and
application.
A. Description
Psychologists seek to describe events and relationships between variables; most often,
researchers use the nomothetic approach and quantitative analysis.
B. Prediction
Correlational relationships allow psychologists to predict behavior or events, but do not allow
psychologists to infer what causes these relationships.
C. Explanation
Psychologists understand the cause of a phenomenon when the three conditions for causal
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inference are met: covariation, time-order relationship, and elimination of plausible alternative
causes.
The experimental method, in which researchers manipulate independent variables to determine
their effect on dependent variables, establishes time order and allows a clearer determination of
covariation.
Plausible alternative causes for a relationship are eliminated if there are no confoundings in a
study.
Researchers seek to generalize a study’s findings to describe different populations, settings, and
conditions.
D. Application
In applied research, psychologists apply their knowledge and research methods to improve
people’s lives.
Psychologists conduct basic research to gain knowledge about behavior and mental processes
and to test theories.
III. Scientific Theory Construction and Testing
Theories are proposed explanations for the causes of phenomena, and they vary in scope and level
of explanation.
A scientific theory is a logically organized set of propositions that defines events, describes
relationships among events, and explains the occurrence of events.
Intervening variables are concepts used in theories to explain why independent and dependent
variables are related.
Successful scientific theories organize empirical knowledge, guide research by offering testable
hypotheses, and survive rigorous testing.
Researchers evaluate theories by judging the theory’s internal consistency, observing whether
hypothesized outcomes occur when the theory is tested, and noting whether the theory makes
precise predictions based on parsimonious explanations.
IV. Summary
REVIEW QUESTIONS AND ANSWERS
These review questions appear in the textbook (without answers) at the end of Chapter 2, and can be
used for a homework assignment or exam preparation. Answers to these questions appear in italic.
1. For each of the following characteristics, distinguish between the scientific approach and everyday
approaches to knowledge: general approach and attitude, observation, concepts, reporting,
instruments, measurement, and hypotheses.
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2. Differentiate between an independent variable and a dependent variable, and provide an example of
each that could be used in an experiment.
3. What is the major advantage of using operational definitions in psychology? In what two ways has the
use of operational definitions been criticized?
4. Distinguish between the accuracy and the precision of a measuring instrument.
Accuracy of a measuring instrument refers to the differences between the reading taken from the
5. What is the difference between the validity of a measure and the reliability of a measure?
6. Which three types of hypotheses lack the critical characteristic of being testable?
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7. Identify the four goals of the scientific method and briefly describe what each goal is intended to
accomplish.
8. Distinguish between the nomothetic approach and the idiographic approach in terms of who is studied
and the nature of the generalizations that are sought.
9. Identify two differences between quantitative and qualitative research.
In quantitative research, a study’s findings are summarized using statistical summaries and analyses.
10. What are researchers able to do when they know that two variables are correlated?
11. Give an example from a research study described in the text that illustrates each of the three
conditions for a causal inference. [You may use the same example for more than one condition.]
The three conditions for a causal inference are: covariation of events; a time-order relationship, that
12. What is the difference between basic and applied research?
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each of 60 rats to one of four conditions differing in the length of time for which the animals were
deprived of food: 0 hours, 8 hours, 16 hours, 24 hours. She then measured the amount of time
the animals spent in the activity wheel in their cages.
B. A physical education instructor was interested in specifying the changes in motor coordination
that occur as children gain experience with large playground equipment (e.g., slides, swings,
climbing walls). For a span of 8 weeks, preschool children were assigned to 4, 6, or 8 hours per
week for time allowed on the equipment. She then tested their motor coordination by asking them
to skip, jump, and stand on one foot.
C. A developmental psychologist was interested in the amount of verbal behavior very young
children displayed depending on who else was present. The children in the study were 3 years
old. These children were observed in a laboratory setting for a 30-minute period. Half of the
children were assigned to a condition in which an adult was present with the child during the
session. The other half of the children were assigned to a condition in which another young child
was present during the session with the child being observed. The psychologist measured the
number, duration, and complexity of the verbal utterances of each observed child.
2. A psychologist conducted an experiment to test the hypothesis that individuals embedded in their in-
group culture would be less likely to help a stranger. College students were recruited to respond to Aa
brief survey about their campus experience@ near the entrance to the student activity center. The first
testing session took place early in the semester. To activate identification with their university
(embeddedness), these participants were given a clipboard and asked to write down three things they
like about their university. Twenty students were tested. The second testing session took place on
two afternoons during the last week of classes at the same location. In this control condition (low-
embedded situation), twenty new students were asked to write down three things they plan to do
during break.
In each condition, immediately after each participant returned the clipboard to the psychologist, a
student research assistant, wearing a sweatshirt with the name of a rival school, walked by the pair
and Aaccidentally@ dropped a file containing papers near the participant. The psychologist recorded
whether the participant helped pick up the papers. Results indicated that, as predicted, participants in
the embedded condition were less likely to help than participants in the control condition. The
psychologist concluded that identification with an in-group (embeddedness) causes people to offer
less help to a stranger.
A. Identify the independent variable of interest to the psychologist (and its levels) and the dependent
variable.
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B. What potentially relevant independent variable is confounded with the psychologist=s
independent variable? Explain clearly how the confounding occurred and describe the
conclusions that can be made about the effects of embeddedness on helping.
C. Suggest ways in which the experiment could be done so the psychologist could make a clear
conclusion about the effect of identification with an in-group (embeddedness) and helping a
stranger.
3. In a widely distributed news report in March 2013, researchers linked 180,000 obesity-related deaths
worldwide (including about 25,000 in America) to the consumption of sugary beverages such as soda,
energy and sports drinks. Using 2010 data from the Global Burden of Diseases Study collected by the
World Health Organization, the researchers investigated obesity-related deaths due to diabetes,
cardiovascular disease, and cancer. They also obtained data for the per-capita consumption of
sugary beverages for the countries in the health study. As sugary-beverage consumption increased,
the risk of obesity-related deaths increased. The researchers claimed that overall, 1 in 100 deaths of
obese people globally is caused by drinking too many sweetened beverages. Prominent nutritionists
have claimed that sugary beverages are a major contributor to the obesity epidemic in the United
States. These data have been used by some government officials to call for limits on the size of soft
drinks (e.g., New York’s Bloomberg law).
A. The researchers claim that consumption of sugary beverages leads to an increased risk of
obesity-related death, and argue that limiting sugary-beverage consumption is an important step
in reducing obesity-related deaths. What evidence from this summary can be used to meet the
conditions necessary for drawing this causal inference and what evidence is lacking?
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B. What sources beyond this summary would you want to check before reaching a conclusion about
these findings? [You might begin with www.cnn.com/2013/03/19/health/sugary-drinks-deaths.]
4. A study was done to determine whether the use of “clickers” as an instructional method would
improve students’ test performance in an educational psychology class (Mayer et al., 2009). In the
clicker class (academic year 2005-‘06), students used clickers to respond to multiple-choice
questions during lectures. In the paper-and-pencil class (2006-‘07), students responded to multiple-
choice questions during lectures using a paper-and-pencil format. In the control condition (2004-‘05),
the instructor did not present multiple choice questions in lectures. Results for the midterm and final
exams indicated that students in the clicker class performed better than students in the paper-and-
pencil and control classes. The researchers concluded that the use of clickers during lectures helps
students to perform better on tests, and suggested that the clickers help students to engage in
appropriate cognitive processing during learning.
A. What evidence is present in this summary to meet the conditions for a causal inference between
the instructional method and students’ test performance? What evidence is lacking? (Be sure to
describe the three conditions for a causal inference.)
B. Identify the four goals of the scientific method and explain whether each is met on the basis of
findings from this study.
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Reading Research Critically
Read the following description of a research study to answer the questions that follow. [Based on the first
experiment in an article by: Griskevicius, V., Tybur, J. M., & Van den Bergh, B. (2010). Going green to be
seen: Status, reputation, and conspicuous conservation. Journal of Personality and Social Psychology,
98, 392-404. doi: 10.1037/a0017346
Status and “Green” Purchases
Why do people purchase environmentally friendly (“green”) products, even when those items may cost
more and may not be as luxurious as non-green products? Griskevicius, Tybur, and Van den Bergh
(2010) argue that one reason may be people’s desire for status. Based on a theory of altruism,
purchasing green products represents a form of self-sacrifice–a choice to forego more luxurious items
and instead make purchases that benefit the environment and society. Furthermore, a person’s ability to
pay more for these items signals to others that he or she has the resources and status to make an
altruistic, green choice. Thus, consumers who choose green products may not be acting entirely
unselfishly; they may perceive an increase in their own social status and prestige when they make green
purchases. Griskevicius et al. refer to this as “competitive altruism.” Based on this theory, these
researchers attempted to “activate” people’s motive (desire) for status to determine if they would then
make more green choices.
To manipulate research participants’ status motives, students (N = 168) who volunteered for the study
were randomly assigned to read one of two stories. In the status condition, students read a story in which
they imagined graduating from college, looking for a job, and then securing a position that offered
opportunities for advancement. Details of the story focused on the high-status features of the workplace.
Previous research with the story indicated that this story successfully increased participants’ desire for
social status and prestige. In the control condition, participants read a neutral story designed not to
enhance desire for status. As they read this story, they imagined losing a concert ticket, searching and
finding it, and then going to the concert. After reading the stories, participants were asked to complete a
“product preference” measure, ostensibly as part of another study. Each participant considered three
types of products (car, household cleaner, and dishwasher), and was asked to choose between a
luxurious version of the product and an environmentally friendly (green) version. Results supported the
researchers’ hypothesis: Participants who read the status story, compared to the control story, were more
likely to choose the green product for each of the three products.
A. What is the independent variable in this study? Identify the specific levels of the independent variable.
B. What is the dependent variable in this study?
C. What information in the summary suggests that the major scientific goal of this study was explanation
(i.e., how people make “green” choices)?
D. How do you think the authors would state the research hypothesis for this study?
2. Examining Correlational Evidence
To help make the point that with only correlational evidence, the investigator can only hypothesize
about possible causal factors underlying a relationship between variables, students can be asked to
identify possible causal factors in the reports below; that is, they are asked to speculate on why
events are correlated. In a preliminary step to research, the investigator considers possible causal
factors, perhaps during discussions with other researchers. As a class or in small groups, students
can speculate on causal factors in the following reports of covariation.
NOTE: To facilitate use for class handouts, the brief reports appear on the next page. Answers for the
brief reports are presented below.
Answers to 2. Examining Correlational Evidence
behavior.
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Examining Correlational Evidence
Instructions: Identify possible causal factors in each of the following reports. That is, why do you think the
events are correlated? Note that by identifying potential causal factors, you are generating hypotheses
regarding the relationships between variables.
A. A number of studies have demonstrated that the type of information posted on job applicants’
Facebook profiles is related to the likelihood the job applicant will be offered a position. For example,
profiles that emphasize family values or professionalism are related to increased likelihood of job
offers, whereas profiles that contain information about use of drugs and alcohol are related to
decreased likelihood of job offers. Why might this occur?
B. Researchers observed students’ lunch and dinner choices at college cafeterias, and then converted
the choices into the number of calories in their meals. When women ate with a male companion, they
chose foods with fewer calories than did women who ate with another woman. Furthermore, the
number of calories women selected decreased as the number of men in their dining group increased.
The number of calories men selected was not related to the presence of men or women.
C. In a study of middle school youth, researchers observed a relationship between popularity and
alcohol use. Popularity was measured by asking students to list five friends (“peer nominations”), and
the number of peer nominations received by each student was summed. Subsequently, students
responded to questions about their alcohol use. As the number of peer-nominated friendships
increased, the likelihood of alcohol use also increased. Why might this occur?
3. Additional Challenge Questions
These challenge questions (along with the concepts illustrated in each question) can be used for
class discussion or possible test questions.
A. Consider how you would respond if you read the following report in a newsletter.
Is your child’s behavior out of control? While considering this question are you reaching for a
cigarette to “calm” your nerves? Before you smoke it, consider this: Researchers investigated
2,356 children from ages 4 to 11 and found a direct link between parents who smoke and children
with behavioral problems. Misbehavior increased with the number of cigarettes smoked by a
parent. Smoking more than a pack a day increased behavioral problems 1.5 times; smoking less
than a pack a day still increased problems 1.4 times. Researchers have several theories to
explain this link, but the bottom line is this: TO IMPROVE YOUR CHILD’S BEHAVIOR, GIVE UP
YOUR SMOKING HABIT.
The last sentence (the italic one) clearly implies a causal relationship between smoking and
children’s behavior. Explain why a causal relationship is not warranted on the basis of this study.
B. A faculty adviser at a small college worked diligently over the summer to prepare an attractive
brochure to give to her advisees when she first met them on campus. The brochure described the
various ways the adviser could be helpful to the students, and the adviser hoped that using the
brochure would increase the number of students who came in to see her early in the semester.
To try to maximize the effectiveness of the brochure the adviser also worked hard at being
especially upbeat and friendly during the first advising meeting with students. Seventy percent of
the students who received the brochure came in to see her more than once, as compared to only
35% of the students who came in to see her the previous year (when no brochure was used). The
adviser concluded that the brochure had the desired effect.
(1) What problem with the way the adviser carried out her study would lead you to be hesitant to
conclude that the brochure was effective?
(2) On the basis of the problem you have identified would you be able to conclude that the
brochure was not effective? Why or why not?
C. One of your friends who is taking introductory psychology this semester tells you about something
her professor covered in class that was a little distressing for her. The professor described a
study dealing with how satisfied married people are in their marriages. The professor emphasized
that the study was very well done. For example, a large sample was used from a well-defined
population and the measures of marital satisfaction were reliable and valid. The finding from the
study that your friend found distressing was that, on average, 65% of the married people
surveyed were less satisfied with their marriage than they had expected they would be. Your
friend is now wondering whether this finding means that she will end up being less satisfied with
her marriage someday.
(1) Identify whether the study described by your friend’s professor in her introductory psychology
class represents the nomothetic or idiographic approach to research in psychology.
(2) Identify whether the study described in your friend’s class represents qualitative or
quantitative research.
(3) How would you respond to your friend’s concern that these research results mean that she
will end up being less satisfied with her marriage if she should someday get married?
D. A physiological psychologist developed a drug that she thought would revolutionize the world of
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horse racing. She named the drug Speedo, and it was her contention that this drug would lead
horses to run much faster than they do now. (For the sake of this hypothetical problem, we are
ignoring the fact that it is illegal to give drugs to racehorses.) She selected two groups of horses
and gave one of the groups injections of Speedo once a week for 4 weeks. Because Speedo was
known to have some negative effects on the horses’ digestive systems, those horses given the
Speedo had to be placed on a special high-protein diet. Those horses not given the Speedo were
maintained on their regular diet. After the 4-week period, all the horses were timed in a 2-mile
race and the mean (average) times for the horses given Speedo were significantly faster than the
mean times for those not given Speedo. The psychologist concluded that her drug was effective.
(1) Identify the independent variable of interest (and its levels) and a potentially relevant
independent variable with which the primary independent variable is confounded. Explain
clearly how the confounding occurred.
(2) State exactly what conclusion about the effect of the drug Speedo can be supported by the
evidence presented.
(3) Finally, suggest ways in which the study could be done so that you could make a clear
conclusion about the effectiveness of the drug Speedo.
E. The New York Times reported the results of a 2-year, $1.5 million study by researchers at
Carnegie Mellon University funded by the National Science Foundation and major technology
companies. There were 169 participants in the study drawn from the Pittsburgh area. The
researchers examined the relationship between Internet use and psychological well-being. A
director of the study stated that the study did not involve testing extreme amounts of Internet use.
The participants were normal adults and their families. On average, for those who used the
Internet the most, psychological well-being was the worst. For example, 1 hour a week of Internet
use led to slight increases on a depression scale and on a loneliness scale and a reported
decline in personal interaction with family members. The researchers concluded that Internet use
appears to cause a decline in psychological well-being. They suggested that users of the Internet
were building shallow relationships that led to an overall decline in feelings of connection to other
people.
(1) The researchers claim that use of the Internet leads to a decline in people’s well-being. What
evidence is present in this summary of the report to meet the conditions necessary for
drawing this causal inference and what evidence is lacking?
(2) What sources beyond this question would you want to check before reaching a conclusion
about the findings reported here? [You might begin with the New York Times piece “The
Lonely Net,” August 30, 1998 and the Washington Post piece “Net Depression Study
Criticized,” September 7, 1998.]
F. A study was done to determine whether taking notes in a developmental psychology course
affected students’ test performance. Students recorded their notes over the entire semester in a
125-page study guide. The study guide included questions on course content covered both in the
textbook and in class lectures. Students’ notes were measured using three dimensions:
completeness, length, and accuracy. Results of the study indicated that students with more
accurate notes performed better on essay and multiple-choice tests in the course than did
students with less accurate notes. Based on these findings, the researchers suggested that
instructors should use instructional techniques such as pausing for brief periods during the lecture
and asking questions to clarify information. The researchers argued that these techniques could
facilitate the accuracy of the notes students take in class, and that accurate note taking could
contribute significantly to students’ overall success in college courses.
(1) What evidence is present in this report to meet the conditions for a causal inference between
accuracy of students’ notes and their test performance? What evidence is lacking? (Be sure
to identify clearly the three conditions for causal inference.)
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method and the goals of research in Chapter 2. Sternberg’s questions are focused for a situation in
which students generate their own research questions. In this assignment students can practice
addressing these questions by applying them to published research reports. There are at least three
ways in which students can identify a published research report. Students can use a reference cited
in a text they have read for one of their psychology courses. Or the instructor can give students a list
of possible articles from which they can choose an article they find interesting. Finally, students can
identify a journal article by doing a literature search following the guidelines described in Chapter 13
in the textbook. Choosing among these three alternatives depends on students’ abilities to use
electronic search techniques and to read journal articles. Once the students have chosen an article
that they find interesting, they then write a brief response to each of the following questions based on
that article.
Alternatively, this exercise can be done in small groups after asking each student to propose a
research question. The instructor may begin by posing a research question (perhaps unknown to the
students) based on a published study.
A. What is the research question the authors are asking in your journal article? What is it about this
question that is interesting to you?
B. Why might this question be scientifically important?
C. To what extent will the science of psychology be advanced by knowing the answer to this
research question?
D. Why would anyone be interested in the results obtained by asking this question?
E. What goal of psychological research (description, prediction, explanation, application) did the
researchers try to meet? Identify one or more aspects of their research methods that allowed you
to make your conclusion.
Students can get feedback on these brief written reports by turning them in to the instructor. Another
option is for students to discuss each of their brief reports in small groups in class to see whether
their fellow students concur that the research questions are important ones.
Reference: Sternberg, R. J. (1997, September). What do students still most need to learn about
research in psychology? APS Observer, 14, 19.
INSTRUCTOR’S LECTURE/DISCUSSION AIDS
The following pages reproduce content from Chapter 2 and may be used to facilitate lecture or
discussion.
1. Psychology Questions: This simple True-False test is designed to pique students’ curiosity regarding
some research findings in psychology. [NB: These questions do not appear in the text.]
2. Answers to Psychology Questions: This page provides answers to the questions posed on the first
page.
3. References for Research Questions: The references for the research cited on the first two pages are
provided on this page.
4. The Scientific Method: This page outlines the differences between the scientific approach to gaining
5. Scientific Observation: This page describes systematic control in experiments through the
manipulation of independent variables.
6. Independent Variables and Dependent Variables: This page asks students to identify independent
and dependent variables in several examples.
7. Constructs and Operational Definitions: This page defines these terms and asks students to match
sample operational definitions to constructs.
8. Measurement: Validity and Reliability: This page defines and contrasts reliability and validity.
9. Testable Hypotheses: This page outlines the characteristics of testable hypotheses.
10. Goals of Research in Psychology: This page identifies the four goals investigators may strive to meet
in their psychological research.
11. Description: Important concepts for the goal of description, nomothetic vs. idiographic research and
quantitative vs. qualitative research, are described on this page.
12. Prediction: On this page correlation and prediction are described.
13. Explanation: Features of the Explanation goal are described on this page, including the three
conditions for causal inference.
14. Confounding: This page explains confounding among variables.
15. Generalization: This page describes researchers’ interest in generalizing the findings of a specific
study to populations, settings, and conditions that were not studied. [NB: The term “external validity”
is used in Chapter 4.]
16. Application: This page describes the difference between basic and applied research.
17. Scientific Theory Construction and Testing: This page identifies key information about theories in
psychology.
18. Intervening Variables: This page describes intervening variables in psychological theories and depicts
the example of “thirst.”
19. Identifying Intervening Variables: This page requires students to identify constructs that could serve
as intervening variables between an independent variable and a dependent variable.
