The Scientific Method
• We don’t always know how people will behave or what they think.
We need to do research.
The Scientific Method
The scientific method
is the way that scientific psychologists gain knowledge about behavior and mental processes.
– The scientific method is not a particular technique or tool.
– Instead, it is a general approach to gaining knowledge.
The scientific method (continued)
We can compare the scientific
method to our “everyday,” nonscientific ways of gaining knowledge on several dimensions:
general approach instruments
– judgments and decisions are based on what “feels right.”
– judgments and decisions
are based on direct observation and experimentation.
– personal biases and
other factors influence observation.
– control is the essential ingredient of science.
– Scientists gain the
greatest control when they conduct an experiment.
Control: Scientists investigate the effect
of various factors one at a time in an experiment.
An experiment has at least one independent
variable and at least one dependent variable.
– Independent Variable (IV): A factor that researchers control or manipulate
in order to determine the effect on behavior.
• A minimum of two levels: The treatment (experimental) condition and the control condition
– Example: In the Pennebaker and Francis (1996) study, the independent variable was whether students wrote about adjusting
to college (experimental condition) or about superficial topics (control condition).
– Dependent Variable (DV): The measure of behavior that is used to assess
the effect of the independent variable.
• Example: In
the Pennebaker and Francis (1996) study on the effects of emotional writing compared to superficial writing, one dependent
variable was students’ Grade Point Average (GPA).
• In most psychology research, several dependent variables are measured to assess the effects of the independent
– For example, Pennebaker and Francis also measured students’
– Personal impressions
– observations and inferences are separate.
– interobserver agreement
– We aren’t clear in the meaning of the words we use.
– For example, what do
we mean by “intelligence”?
– Define specifically what we mean by our concepts
– A construct is a concept or idea used in psychological theories.
• There are many psychological constructs.
Examples: aggression, depression, emotion, intelligence, memory, personality, stress,
• An operational definition is the specific procedure used to
produce and measure a construct.
Advantages of operational definitions:
– Allow scientists to define specifically what they mean by their construct
– Allow clear communication among scientists.
– A potentially limitless number of operational definitions exists for
any particular construct.
– Some operational definitions may be meaningless.
– for example, diaries,
gossip, rumors and opinions
– Accuracy: difference between what an instrument says and what is actually true
– Precision: measures have different levels of precision.
Not valid or reliable
– measures of our concepts
that are inaccurate or inconsistent.
Valid and reliable
– valid measures get at the truth,
– reliable measures are consistent.
• Physical measurement involves dimensions that have agreed-upon standards and instruments.
– Examples: length, weight, time
• Psychological measurement is used to measure constructs for which there is no agreed upon standard or instrument.
– Are there agreed upon standards for what is considered beauty,
intelligence, or aggression?
Psychologists develop measures to assess
these and other psychological constructs.
• Measures must be valid and reliable.
– Validity refers to truthfulness; a valid measure is one that measures what it claims to measure.
• Example: Does the SAT actually measures skills necessary
for success in college?
– Reliability refers to the consistency of a measure.
• For example, a measure is considered reliable when different observers consistently agree about an observation.
– Note that a measure may be reliable but not valid.
• For example, a scale that consistently underreports someone’s weight is reliable but not valid.
– concepts not defined clearly,
– appeals to ideas outside realm of science.
– concepts are clearly defined and can be measured.
Hypotheses are not testable if they
have any of these three characteristics:
– Constructs are not adequately defined.
Example: People become aggressive following exposure to media violence because the violence is “disturbing.”
– The hypothesis is circular — the event itself is used as an explanation of the
• Example: People become aggressive following exposure to media violence because they become
verbally or physically abusive.
– The hypothesis appeals to ideas or forces that are not recognized by science.
• Example: People become aggressive following exposure to media violence because of psychic
– accept claims with insufficient
evidence, ignore contradictory evidence
– behavior and mental processes are complex,
– human mistakes are made
(even in science).
Goals of the Scientific Method
• Researchers use the scientific method to meet four research goals:
• Researchers define, classify, catalogue, or categorize events and
their relationships to describe mental processes and behavior.
– Example: Psychologists describe symptoms of depression. One operational definition of depression comes from the list of
symptoms in the Diagnostic and Statistical Manual.
psychology research is nomothetic rather than idiographic.
– Nomothetic: large sample sizes, “average” performance of a group
– Idiographic: individual case studies
– Nomothetic researchers appreciate there are important differences among individuals;
they seek, however, to emphasize similarities among individuals.
psychology research is quantitative rather than qualitative.
– Quantitative: statistical summaries of performance
– Qualitative: verbal summaries of research findings
• When researchers identify correlations (relationships) among variables,
they are able to predict mental processes and behavior.
– Example: As level of depression increases, individuals exhibit more helplessness (failure to initiate activities and pessimism
regarding the future).
• A variable is a dimension on which people differ, or vary.
– Examples: childhood loss of parent (yes/no), symptoms of depression, aggressiveness, age, emotional problems, stressful
life events, physical illness
A correlation occurs when two measures
of the same people, events, or things vary together or go together.
– Example: The more stressful life events a person experiences (one variable), the more likely they are to experience physical
illness (a second variable).
• When two variables are correlated, if we know people’s scores
for one variable, we can statistically compute (predict) their scores for the second variable.
– For example, if we know the extent to which someone has experienced life stress, we
can compute their likelihood of experiencing physical illness (and predict stress based on illness).
– Because test scores (SAT, GRE) are correlated with grades, we can predict students’
grades based on knowing their test scores (and predict test scores from grades).
Correlation does not imply causation. We don’t know why the variables are correlated.
For example, there’s a correlation
between the amount of hair in one’s ear and the presence of heart disease. (true)
– Does this mean that having hair in one’s ears causes heart disease?
– Does this mean that having heart disease causes hair to grow in the ears?
– Or is there some other variable that accounts for the relationship between ear hair
and heart disease?
• Researchers understand and can explain a phenomenon when they can
identify its cause(s).
– Example: Research participants exposed to unsolvable problems become more pessimistic and less willing to do new tasks
(i.e., they become helpless) than participants who are asked to do solvable problems.
Researchers conduct controlled experiments
to identify the causes of a phenomenon.
requires that researchers manipulate factors, one at a time, to determine their effect on the event of interest
— these are independent variables.
Researchers observe the effect of the independent
variable by measuring dependent variables.
• Remember: The word “experiment” is often used in everyday language
to mean the same thing as “research,” but the word experiment refers to a very specific type of research
Using experiments, researchers can make
causal inferences — statements about the cause of an event or behavior.
Three conditions for making a causal inference:
1. Covariation of events: If one event causes the other, the two events must vary together (when one changes,
the other must change also).
2. Time-order relationship: The presumed cause must occur before the presumed effect.
3. Elimination of plausible alternative causes: We accept a causal explanation only when other possible causes
of the effect have been ruled out.
Example of a causal inference based on
Exposure to media violence causes an increase
in the likelihood of aggressive and violent thoughts, emotions, and behaviors immediately after the exposure.
Based on this research, we know
– Exposure to media violence and aggression vary together.
– Aggression follows after the exposure (not before).
– Other explanation for the relationship between exposure to media violence and aggression
have been ruled out.
• Causal Inferences
– Scientific control requires that the effects of independent variables are isolated.
– A confounding occurs when two potentially effective independent variables are
allowed to vary together simultaneously — we cannot determine which variable caused the effect on the dependent variable.
– When an experiment is free of confoundings, we can make a causal inference regarding
the effect of the independent variable on the dependent variable.
Researchers are not interested just in
the one sample of people or the one set of circumstances they tested.
They wish to generalize a study’s
findings to different populations, settings, and conditions beyond those used in the specific study.
– Can we generalize or apply the findings from psychology studies with college students
samples to other people?
– Can we generalize the findings of highly controlled laboratory studies to real-world
– For example, can a study that examines conditions of aggression in the lab with college
students be used to understand real-life conditions of aggression?
• Psychologists apply their knowledge and research methods to improve
– Example: Treatment that encourages depressed individuals to attempt tasks that can be mastered or easily attained decreases
depressives’ helplessness and pessimism.
Basic and Applied Research
– Applied Research:
Psychologists conduct research to change people’s lives for the better.
Applied research is often conducted in “real world” or natural settings.
– Basic Research:
Psychologists conduct research to understand behavior and mental processes — “seeking knowledge for its own sake.”
Basic research is often carried out in laboratory settings with the goal of testing theories.
Both basic and applied research studies
Scientific Theory Construction
Theories are proposed explanations for
the causes of phenomena.
– Theories attempt to explain the who, what, when, where, how,
and why of people’s behavior and mental processes.
– A theory is a logically organized set of statements that
• define events (concepts),
• describe relationships among these events, and
• explain the occurrence of these events.
– Theories vary in their
scope and complexity.
– Successful theories
• organize what we know about a behavior or mental process (empirical knowledge),
• guide future research by suggesting testable hypotheses, and
• survive rigorous testing (such as falsification).
– Good theories are logical and internally consistent, precise, and
Theories are Parsimonious
• No way to win in defining scope of study
• If theory is too broad
– Not easy to measure constructs
– Not easy to put into practice
• If theory is too narrow
– May not explain all necessary events
– Theories often propose intervening processes or mechanisms to explain
the relationship between an independent variable and a dependent variable.
– Intervening variables
are “hidden” processes that are represented by psychological constructs.