Why Psychologists Conduct Experiments Variables & Methods

Variables & Methods Why Psychologists Conduct Experiments

Psychology 280 Lecture ƒ Test hypotheses derived from theories
Orange Coast College ƒ Test the effectiveness of a treatment or program
ƒ Experiments differ from other research designs because they
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allow researchers to determine the causes of behavior.

ƒ What were the goals of science?

ƒ Describe behavior
ƒ Predict behavior
ƒ Determine the causes of behavior
ƒ Explain behavior

Variables Variables (con’t)

ƒ A variable is any event, situation, or behavior that varies. ƒ Four general classifications

ƒ Key properties of variables 1. Situational variables describe characteristics of a situation or
the environment.
ƒ Specific instances will vary – called values or levels
ƒ Will have at least two levels 2. Response variables are the responses or behaviors of
ƒ Will have true numeric properties OR individuals.
ƒ Will have non-numeric properties that usually identify different
3. Participant or subject variables are individual differences.
categories
4. Mediating variables are psychological processes that
mediate the effects of a situational variable on a particular
response. Example: Kitty Genovese and diffusion of
responsibility

Main Types of Designs Main Types of Designs (con’t)

ƒ Descriptive (Nonexperimental) ƒ Quasi-experimental design

ƒ Describe the characteristics of an existing phenomenon ƒ Test for causal relationships among variables without having full control
ƒ Little to no control over variables; no variables manipulated ƒ No variables manipulated or random assignment (observed)
ƒ No cause and effect ƒ Moderate control over variables
ƒ Results are suggestive, but trouble concluding cause and effect
ƒ Historical (Nonexperimental)
ƒ Experimental design
ƒ Relate events that have occurred in the past to current events
ƒ Little to no control over variables; no variables manipulated ƒ Test for true cause and effect relationships
ƒ No cause and effect ƒ Manipulating variables
ƒ Randomly assigning participants into conditions
ƒ Correlational design (Nonexperimental) ƒ High control over variables
ƒ Reach better conclusions about cause and effect
ƒ Examine the relationship between variables
ƒ Low to medium control over variables; no variables manipulated 1
ƒ No cause and effect

Experimental Research Experimental Research

ƒ An experiment must include: ƒ Dependent variables are

„ an independent variable (IV) and „ measured by the experimenter, and
„ dependent variable(s) (DVs). „ are used to determine the effect of the Independent

ƒ An Independent Variable Variable.
„ In most experiments, researchers measure several
„ is manipulated (controlled) by the experimenter, and
„ has at least two different conditions dependent variables to learn the effect of the
independent variable.
(e.g., “treatment” and “control” conditions).

Examples of Experimental Research Review: Nonexperimental
ƒ Let’s watch the Psychologist and the Experiment Versus Experimental Methods

ƒ Nonexperimental method

• Relationships studied using observations or
measures of the variables of interest

• Problems with making causal statements using this
method

9Think back to our discussion on the goals of science and

determining the causes of behavior. What are the problems with
the nonexperimental approach?

Review: Nonexperimental Versus Review: Nonexperimental Versus
Experimental Methods Experimental Methods

ƒ Nonexperimental method (con’t) ƒ Experimental method

• There are two problems with making causal ƒ One variable is manipulated and the other variable
statements measured
ƒ(coAntftoeumnpdtisngto) eliminates the third variable problem
1. Direction of cause and effect
e- nEvxirpoenrmimeennt)tal control (example: controlling
• Temporal precedence; Covariation of cause & effect c- oRntarnodllionmgipzaartitoicnip/raanntdcohmaraascsteigrnismticesn)t (example:

2. Third variable problem

• Elimination of alternative explanations

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Relationships Between Variables Relationships Between Variables (con’t)

ƒ Relationships between two variables For the purposes of describing relationships, we will
ƒ Do the levels of the two variables vary systematically use variables that have true numeric properties.
together?
Interval scale of measurement
Example: As the number of days absent increases, do grades in Ratio scale of measurement
the class decrease also?

Relationships Between Variables (con’t) Relationships Between Variables (con’t)

ƒ Positive linear relationship (covary in the ƒ Negative linear relationship (covary in opposite
same direction). directions)

Relationships Between Variables (con’t) Relationships Between Variables (con’t)

ƒ Curvilinear relationship – increases in one variable ƒ No relationship between the variables
produce both increases and decreases in another variable

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Relationships Between Variables (con’t) Review: Independent and
Dependent Variables
ƒ Research uses a variety of research designs to identify
systematic relationships between variables. ƒ Independent variable (IV)
ƒThe better the research design, the less random error
measured and the less uncertainty you will have attributing ƒ Manipulated variable (cause)
cause and effect
ƒSome are participant variables that are not
ƒThe experimental design is the strongest of these designs due to experimentally manipulated
its control features
ƒ Dependent variable (DV)

ƒ Measured variable (effect)

ƒ Many are abstract constructs (stress, mood,
cognitive performance)

Review: Independent Review: Causality
and Dependent Variables
ƒ The inferences of cause and effect require three
ƒRemember that in the experimental method……. elements

• One variable is manipulated (IV) and the other 1. Temporal order
variable measured (DV) 2. Covariation between the two variables

ƒ IV = cause; DV=effect
3. Need to eliminate plausible alternative explanations

Operational Definitions of Variables Developing IV’s & DV’s

ƒ Variable is an abstract concept that must be translated into ƒCreate a operational definition for your independent
concrete forms of observation or manipulation. variable(s) and dependent variable(s)
ƒChoose the range of your independent variable
ƒ A variable must be defined in terms of the specific method
used to measure or manipulate it. ƒFind a realistic range
ƒSelect a range that shows effect
ƒ This is called the operational definition. ƒA good idea is to do a pilot experiment (not
required for class experiment)
ƒ How do you define “STRESS” ?

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Developing IV’s & DV’s (con’t) Developing IV’s & DV’s (con’t)

ƒThe dependent variable needs to be reliable and valid ƒSuppose you are interested in memory and want to
compare two ways of presenting material to be
ƒReliable = getting the same results when the remembered.
measurement is repeated multiple times
ƒAfter one week you wish to measure how much your
ƒValidity = measuring what we intend to measure subjects remember. What should you measure?

ƒThe closer you come to directly observing the behavior ƒAsk them what they remember?
you are interested in, the less controversy (in terms of
reliability and validity) you will have ƒWhat if they can’t remember anything? Does that mean they
remember nothing?

Developing IV’s & DV’s (con’t) Example: Writing About Emotional
Experiences
ƒCould you use a recognition test and determine the accuracy
at picking previously presented material? ƒ Pennebaker and Francis (1996) had several research
questions:
ƒCould you have them relearn the material and measure the
percent of time saved by having learned it before? ƒ Does writing about emotional experiences cause people to
experience better outcomes?
ƒWhat type of results do you think each of these methods
might give you? ƒ [Note: Better than what? We need a comparison. That’s why we have
control groups.]
ƒConsideration: Dependent variables, even those that
appear to be directly observable, may be linked only ƒ Are cognitive changes that occur with writing about emotional
indirectly to the behavior you are interested in experiences related to these outcomes?

Research Example (continued) Research Example (continued)

ƒ Pennebaker and Francis manipulated an independent ƒ They measured several dependent variables to
variable, type of writing, using two levels (or conditions):
operationally define “outcome” and “cognitive changes”:
ƒ emotional writing
ƒ operationally defined as writing “about your deepest thoughts ƒ Health outcome was measured by the number of physician visits.
and feelings about coming to college” ƒ Academic outcome was measured using students’ Grade Point

ƒ superficial writing Average (GPA).
ƒ operationally defined as describing “in writing any particular ƒ Cognitive change was measured using language frequency
object or event of your choosing…as objectively and as
dispassionately as you can…” counts (e.g., number of “insight” and “understand” words).

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Research Example (continued) Research Example: Causal Inferences

ƒ Pennebaker and Francis’ hypotheses: ƒ Three conditions must be met before we can make a causal inference:

ƒ Students in the emotional writing condition will have ƒ Covariation of cause and effect: We must observe a relationship
better health and academic outcomes than students in between the independent and dependent variables.
the superficial writing condition. For example, participants who write about emotional events have
better health and academic outcomes than participants who
ƒ Students in the emotional writing condition, compared to write about superficial events.
the superficial writing condition, will demonstrate ƒ Thus, the two types of writing covary with the different
cognitive change (i.e., more insight and understand outcomes.
words). ƒ Is this enough????

ƒ As we’ve learned, covariation is not enough for making a causal
inference (“correlation does not imply causation”). More is needed.

Causal Inferences (continued) Causal Inferences (continued)

ƒ Temporal precedence: The presumed cause precedes the ƒ Elimination of alternative explanations: Using control
effect. techniques, we rule out other possible causes for the
outcome.
For example, writing about emotional events (the cause) comes
before the beneficial health and academic outcomes (the effect). ƒ If the two groups differ in ways other than the emotional and
superficial writing, these differences become alternative
ƒ Establishing a time-order relationship can be tricky. explanations for the study’s findings.

ƒ An important question to ask is: ƒ To eliminate alternative explanations, researchers use two
main control techniques:
How can we be sure that participants in the emotional writing ƒ holding conditions constant, and
condition were not healthier and more academically successful ƒ balancing.
(e.g., higher GPA) than the superficial writing participants before
they even wrote one word? (i.e., the effect precedes the cause)? ƒ With proper use of control techniques, an experiment has
internal validity (we will discuss this much later in class)

Choosing A Method: Advantages of Choosing A Method: Advantages of
Multiple Methods Multiple Methods

ƒ Research findings based on a single method for making ƒ Experimental versus nonexperimental methods
observations may be biased because of characteristics of the
measurement process. • Considerations

ƒ A multimethod approach means that researchers use a variety of 1. Artificiality
measures to examine a research question: 2. Ethical and practical issues
3. Participant variables
ƒ Direct observation 4. Description of behavior
ƒ Surveys 5. Successful predictions for the future
ƒ Unobtrusive measures 6. Advantages of multiple methods

ƒ Because direct observation and survey methods can be reactive
(i.e., people react to being observed), unobtrusive measures provide
an important alternative for gaining information about people.

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Evaluating Research: Three Validities The End

ƒ Construct validity – the adequacy of the operational
definitions

ƒ Internal validity – the ability to draw conclusions
about causal relationships

ƒ External validity – the extent to which the results
can be generalized to other populations and
settings

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