1. science
2. mathematics
3. statistics

Psychology (8th Edition) – David Myers
Chapter 1 – Thinking Critically with Psychological Science
“What good fortune for those in power that people do not think.” – Adolf Hitler (1889-1945)
The Need for Psychological Science
 How can we best use psychology to understand why people think, feel, and act as they do?
 Psychology needs a scientific approach to separate “common sense” and “hunches” from actual credible evidence
Limits of Intuition and Common Sense
 Intuition and common sense are not credible sources (differs from person to person) and seem correct after the
fact (“I knew it all along…”)
o “The naked intellect is an extraordinarily inaccurate instrument.” – Madeleine L’Engle (1977)
Did We Know It All Along? Hindsight Bias
 Hindsight is 20/20 – after the fact, it is easy/more clear to see why an event occurred, someone acted a certain
way, etc
 Hindsight bias – (“I knew it all along” phenomenon) the tendency to believe, after learning an outcome, that one
would have foreseen it.
o give one group one phenomenon (ex: “Absence makes the heart grow fonder”) and they will find
overwhelming evidence and support for the statement and claim it is common sense.
o give another group the opposite phenomenon (ex: “Out of sight, out of mind”) and they will also find
overwhelming evidence and support for the statement and claim it is common sense.
o Problem: how can opposite statements both be supported as “common sense?”
 Common sense describes more easily what has already happened than it can predict what will happen in the
future.
 However, psychological findings may seem like common sense because we have observed some behaviors
constantly.
 Things that seem like common sense or that we have taken as fact (eg: dreams predict the future, emotions are
linked with menstrual cycles) are in many cases proved wrong by psychological research
Overconfidence
 Humans tend to be overconfident (we tend to think we know more than we do).
 Before presented with a task, it is predicted that it will be completed much quicker than it actually will be. After
presented with the task and while completing the task, overconfidence becomes apparent.
o Before a test, a student can feel overconfident, but when presented with the test, the reality sets in.
 Even after presented with the task and solutions, most will claim, “Well, I was almost right.”
*** Hindsight bias and overconfidence often lead us to overestimate our intuition. But scientific inquiry, fed by curious
skepticism and by humility, can help us sift reality from illusions. ***
The Scientific Attitude
 Curiosity underlies all science… the desire for more knowledge.
 No matter how crazy an idea or hypothesis sounds… the questions are: does it work? When put to the test, can its
predictions be confirmed?
o Things that we take as granted now, were once considered crazy (eg: the earth revolves around the sun,
meteorites are from outer space, the earth is round) but were proven true with scientific inquiry.
 To sift the reality from the fantasy, a scientific attitude is required
o being skeptical but not cynical, open but not gullible.
o Humility – being humble, often scientists must reject their own ideas/hypotheses (“The rat is always
right.”)
 Critical thinking – (smart thinking), thinking that does not blindly accept arguments and conclusions; rather is
examines assumptions, discerns hidden values, evaluates evidence, and assesses conclusions.
o Asking questions – how do you know this? Is there an agenda here? Is the conclusion based on evidence
not a hunch? Are there any alternative conclusions?
The Scientific Method
 Scientific method: a method in which scientists make observations, form theories, and then refine theories in the
light of observations.
 Theory – an explanation using an integrated set of principles that organizes and predicts observations
o Can organize a set of conclusions and findings that can be helpful in predicting future actions.
o Must be put to the test before accepted as fact  must produce testable predictions (hypotheses)
 Hypothesis – a testable prediction, often implied by a theory
 When testing hypotheses, it is important to be aware of biased observations and conclusions (looking for the
desired/predicted outcomes regardless of the actual results). Psychologists publish their work to so it can be
checked by other psychologists in order to see if the same results and outcomes are gathered.
 For findings to be reliable and valid, psychologists must report their research with precise operational definitions
so other psychologists can replicate their observations.
o Operational definitions – a statement of the procedures/operations used to define research variables
(eg: human intelligence can be operationally defined as what an intelligence test measures.)
o Replication – repeating the essence of a research study, usually with different participants in different
situations, to see whether the basic finding extends to other participants in other circumstances
1) Theories
Generate
or refine…
Lead to…
3) Research and
Observations
2) Hypothesis
Lead to…

For a theory to be useful, it MUST…
o Effective organize a range of self-reports and observations
o Imply clear predictions that anyone can use to check the theory or to derive practical applications.
Description
 Description is the starting point of any science – types of research methods that describe behaviors/attitudes, not
explains them
The Case Study
 Case study – an observation technique in which one person is studied in depth with the hope of revealing
universal principles.
o For example: long term brain studies in individuals and developmental studies of individuals
 Pros
o Can suggest further hypotheses for the future
o Can show what might happen (if generalized to a larger population)
 Cons
o Individual case studies can be misleading and not representative of the general population
The Survey
 Survey – a technique for ascertaining the self-reported attitudes or behaviors fr people, usually by questioning a
representative, random sample of them.
o Gallop polls, Kinsey Report
 Results are largely based on how questions are worded and interpreted by individuals
o Eg: people are more likely to “not allow” something rather than “forbid” or “censor”; “aid to the needy”
instead of “welfare;” “revenue enhancers” instead of “taxes”
 Surveys use random sampling to chose participants in an aim to get the most representative results
o False consensus effect – the tendency to overestimate the extent to which others share our beliefs and
behaviors
 Vegetarians think there are far more vegetarians than in reality; conservatives believe more
support for their beliefs than liberals
o Random representative sampling avoids the false consensus effect and produces results that can be
generalized to a larger population
 Population – all the cases in a group, from which samples may be drawn for a study
 Random sample – a sample that fairly represents a population because each member has an
equal chance of inclusion in the study
 Large representative samples are better than smaller ones
 Pros:
o Can look at many cases and individuals
 Cons:
o Results can differ based on wording
o Need large populations and appropriate sampling groups
o Self-reporting can be unreliable
Naturalistic Observation
 Naturalistic observation – observing and recording behavior in naturally occurring situations without trying to
manipulate and control the situation.
o Eg: watching chimpanzee societies in the jungle, videotaping and analyzing parent-child relationships in
different cultures, recording students’ self-seating patterns in the lunchroom of multiracial schools
 Observers must be careful not to attempt to change or control the situation… need authentic observations for
authentic and reliable descriptions
Correlation
 Correlation – a measure of the extent to which two factors vary together, and thus of how well either factor
predicts the other – how are two things related? How strong is this relationship? Can the relationship shape
predictions?
 Correlation coefficient – the mathematical expression of the relationship, ranging from -1 to +1
o Measures how well either one predicts the other and how strong that relationship/prediction is
o Eg: r = +0.37
 r  correlation coefficient (relationship)

 +  indicates direction of relationship (positive or negative)
 0.37  Indicates strength of relationship (0.00 to 1.00)
Scatterplots – a graphed cluster of dots, each of which represents the values of two variables. The amount of
scatter suggests the strength of the correlation (little scatter = more correlation)
o Positive correlation – two variables rise or fall together (the taller you are the more you weigh)
o Negative correlation – two variables relate inversely (the more you brush your teeth, the less cavities you
will have)

-1.00
+1.00
0.00
Correlations cannot fully predict future behaviors/attitudes
o Children of abusive parents tend to abuse their children, however not all abused children abuse their
children later in life.
Correlation and Causation
 Correlation does not mean causation, no matter how strong the correlation coefficient is.
o Eg: low self esteem is correlated with depression, however this does not mean that low self esteem
particularly causes depression
(1) Low self esteem
Could cause
Depression
OR
(2) Depression
Could cause
Low self esteem
OR
(3) Distressing
events or biological
predisposition
Depression
Could cause
+
Low self esteem

Correlation indicates the possibility of a cause-effect relationship, but it does not prove causation.
Illusory Correlations
 Illusory correlation – the perception of a correlation where none exists
o Eg: Being cold and wet causes one to catch a cold
Perceiving Order in Random Events
 Humans tend to perceive order in random events… we want order! We want to make sense and organize
events!

Random coincidences often don’t look random.
Your chances of being dealt either of these hands
are precisely the same: 1 in 2,598,960.

Patterns and sequences occur naturally in random data, but we tend to interpret these patterns as meaningful data.
Experimentation
Exploring Cause and Effect
 Because many factors influence everyday behaviors/attitudes, psychologists need to isolate and control variables
to establish cause and effect relationships  the clearest way to do this is by experimentation
 Experiment – a research method in which an investigator manipulates one or more factors (independent
variables) to observe the effect on some behavior or mental process (the dependent variable). By random
assignment of participants, the experimenter aims to control other relevant factors.
o Manipulate the factors of influence
o Hold other variables constant
o Unlike correlational studies that uncover naturally occurring relationships, an experiment manipulates a
factor to determine its effect.
Evaluating Therapies
 Our tendency to seek new remedies when we are ill or emotionally down can produce misleading testimonies.
o Eg: if three days into a cold, we start taking vitamin C tablets and find out cold symptoms lessening, we
may credit the pills rather than the cold naturally subsiding.
 To find out if a treatment is actually effective, we have to test it with experimentation.
 In many studies, participants are blind (uninformed) about what treatment, if any, they are given.
o One group receives the actual treatment.
o One group receives a pseduotreatment – an inert placebo (eg: a pill with no medicine, a sugar pill)
o If a treatment is effective, the group receiving the real treatment should see positive results, while the
other group shows no change.
 If neither the participant nor the researcher collecting data are aware of which groups receive which treatment, it
is called a double-blind procedure/study.
o Double-blind procedure/study – an experimental procedure in which both the research participants and
the research staff are unaware about whether the research participants have received the treatment or a
placebo.
o Allows researchers to check a treatment’s actual effects apart from 1) the researchers anticipated results,
and 2) the research participants’ enthusiasm for the treatment and the belief that it will heal.
 Placebo effect – experimental results caused by expectations alone; any effect on behavior caused by the
administration of an inert substance or condition, which is assumed to be an active agent.
o Participants receiving the placebo (fake treatment) may report positive results because they believe the
drug is real and active.
 The double blind study is one way to create an experimental condition in which people receive the treatment and a
contrasting control condition without the treatment.
o Experimental condition – the condition of an experiment that exposes participants to the treatment, that
is, to one version of the independent variable.
o Control condition – the condition of an experiment that contrasts with the experimental condition and
serves as a comparison for evaluating the effect of the treatment.
 Researchers randomly assign people these conditions to be certain the two groups are otherwise identical.
o Random assignment – assigning participants to experimental and control conditions by chance, thus
minimizing preexisting differences between those assigned to the different groups.
Independent and Dependent Variables
 Independent variable – the experimental factor that is manipulated; the variable whose effect is being studied
 Dependent variable – the outcome factor; the variable that may change in response to manipulations of the
independent variable.
 Example: Scientists hypothesize that children who drink breast milk as babies are more intelligent later in life
compared to babies who don’t drink breast milk. To study the relationship between breast milk consumption and
intelligence, the experimental group is given breast milk while the control group is given formula. 8 years later,
the children are given an intelligence test to measure any differences in intelligence levels.
o Independent variable: type of milk consumed; breast milk and formula – this variable is the one purposely
manipulated.
o Dependent variable: intelligence – the outcome; the variable that may change in response to
manipulations

Variable – anything that can vary
Research Method
Descriptive
Correlational
Experimental
COMPARING RESEARCH METHODS
Basic Purpose
How Conducted
What is
Manipulated?
To observe and
Case studies,
Nothing
record behavior
surveys, or
naturalistic
observations
To detect naturally
Compute statistical
Nothing
occurring
association,
relationships; to
sometimes among
assess how well one
survey responses
variable predicts
another
To explore cause and Manipulate one or
The independent
effect
more factors; random variable(s)
assignment to groups
Weakness
No control of
variables; single
cases may be
misleading
Does not specify
cause and effect
Sometimes not
feasible; results may
not generalize to
other contexts; not
ethical to manipulate
certain variables
*** Note the difference between random sampling and random assignment. Random sampling is used during surveys to
help generalize results to a larger population. Random assignment is used during experiments to control outside influences
and present clear cause and effect relationships. ***
Statistical Reasoning
 After gathering dating with research methods, it needs to be organized and summarized using statistics so we can
make inferences about the data.
o Popular and off-the-top-of-the-head estimates can be misread and construed. (Eg: One percent of
Americans (2.7 million) are homeless. Or is it 300,000, an earlier estimate by the federal government? Or
600,000, an estimate by the Urban Institute?
o Doubt large, round, and undocumented numbers.
Describing Data
 Once research is complete, the data needs to be organized.
Measures of Central Tendency
 measure of central tendency – a single score that represents a whole set of scores/data
o Mode – the most frequently occurring score in a distribution.
o Mean – the average of the distribution (add the scores and divide by the number of scores)
o Median – the middle score in a distribution; half the scores are above it and half are below it.
 Neatly summarize data, but does not account for data that is lopsided or skewed.
 Always note which measure of central tendency is being reported. If it is a mean, then consider whether a few
atypical scores could be distorting it.
 Eg: 10,11,11,12,14,15,15,15,16
o Mode: 15
o Mean: 13.2
o Median: 14
Measures of Variation
 There is also value of knowing the variation within a data set (how similar or diverse the scores are).
 Range – the difference between the highest and the lowest scores in a distribution.
 Standard deviation – a computed measure of how much scores vary around the mean score.
σ=
Sum of (deviations)2
Number of scores
*** In a typical distribution of numbers, about 68% of all the scores will be within 1 standard deviation above or below
the mean, and about 95% of all scores are within 2 standard deviation scores above or below the mean.***
Making Inferences
When Is An Observable Difference Reliable?
 When deciding if it is safe to generalize from a sample, keep three principles in mind.
o Representative samples are better than biased samples.
 For results to be generalized, the group sampled must be representative of the population that it
aims to generalize.
o Less-variable observations are more reliable than those that are more variable.
 An average/mean is more reliable when it comes from a data set with low score variability. (eg:
11,12,13,13,14,15 has a more reliable mean than 10,23,65,90,95,100)
o More cases are better than fewer.
 Averages based on many cases are more reliable than averages based on only a few cases. All
cases need to be representative of the population studied.
When Is A Difference Significant?
 When averages from two samples are each reliable measures of their respective populations, then their difference
is likely to be reliable as well.
o Eg: The less the variability in women’s and in men’s aggression scores, the more confidence we would
have that any observed gender difference is reliable.)
 When the sample averages are reliable and the difference between them is relatively large, the difference has
statistical significance.
o Statistical significance – a statistical statement of how likely it is that an obtained result occurred by
chance.
o Statistical differences indicate the likelihood of a result’s occurring, not the importance of the result.
Frequently Asked Questions About Psychology
Can Laboratory Experiments Illuminate Everyday Life?
 Do experiments that test seemingly random things (eg: our ability to remember a sequence of terms/numbers, how
fast a person can associate colors with words, etc) actually have relevance to everyday life?
 Experiments aim to be simplified reality, with elements that are controlled and held constant while other elements
are manipulated.
 There is less concern with the particular behaviors in an experiment, but rather interest in the general principles
that can help explain behaviors.
Does Behavior Depend on One’s Culture?
 Culture – shared behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted
from one generation to the next.
 Being aware of one’s beliefs, values, and cultural traditions can help shed light on the reason behind
attitudes/behaviors.
 However, because of a shared biological heritage, there are principles that are universal for all humans.
 “People are all the same; only their habits differ.” – Confucius (551-479 BCE)
Does Behavior Vary With Gender?
 Gender issues and differences permeate psychology, however psychologically and biologically, men and women
are mostly similar.
Why Do Psychologists Study Animals?
 Animals are studied for various reasons…
o To understand how different species learn, think, and behave
o To learn more about people, by doing experiments that are permissible only with animals. Human
physiology resembles that of many other animals.
o Treatment for other diseases
Is It Ethical To Experiment On Animals?
 The amount of animals experimented on or killed is a fraction of 1% of the number of animals killed globally for
food. Annually, 200,000 cats and dogs are used in experiments (under humane regulations) while animal shelters
kill 50 times that many.
 Groups like Psychologists for the Ethical Treatment of Animals advocate for naturalistic observation of animals
rather than laboratory manipulation.
 Experiments on animals have produced incredibly important results, like vaccines and cures for diseases.
 Thoughts on the morality of testing on animals differ from culture to culture.
 Is it right to place the well-being of humans over that of animals?
 Research has shown that humans value certain animals over others, possibly based on their likeness to humans.
(primates valued, while rats seem not to be)
 Most researchers feel ethically obligated to enhance the well-being of captive animals and protect them from
needless suffering.
 Many professional associations and funding agencies have guidelines for the humane use of animals.
 Not only do humans benefit from animal testing, but animals have benefited as well.
Is It Ethical to Experiment on People?
 Psychological research on people typically involves nothing further than blinking lights, flashing words, and
pleasant social interactions.
 Occasionally, researchers intentionally temporarily induce stress and deceive people, but only when they believe
it is essential to a justifiable end.
 Ethical procedures developed by the American Psychological Association and the British Psychological Society
urge investigators to…
o Obtain the informed consent of potential participants
o Protect them from harm and discomfort
o Treat information about individual participants confidentially

o Fully explain the research afterward (debrief)
Much research takes place outside of laboratories and universities, for example in retail stores that conduct
surveys, photograph purchases, track buying patterns, and test advertising effectiveness.
Is Psychology Free of Value Judgments?
 Psychology is not value-free. Researchers’ values influence their choice of research topics.
 Values can also “color the facts” – our preconceptions can bias our observations and interpretations (we see what
we want or expect to see)
 In and out of psychology, labels describe and labels evaluate.
Is Psychology Potentially Dangerous?
 Knowledge can be used for good or evil… psychologists have ethical standards to follow to ensure that people are
not manipulated for the worse.