2. Constants vs. Variables
Characteristics of the psychological situations
Constants: have the same value for all individuals in
the situation
Variables: have potentially different values for each
individual in the situation
3. Variables
Conceptual vs. Operational
Conceptual variables (constructs) are abstract
theoretical entities
Operational variables are defined in terms within
the experiment. They are concrete so that they can
be measured or manipulated
4. Variables
Independent variables (explanatory)
Dependent variables (response)
Extraneous variables
Control variables
Random variables
Confound variables
Simplest study has one independent variable and
one dependent variable
11. Types of Variables
independent variable (IV)…
what you (or nature) manipulates in some way
dependent variable (DV)…
what you presume to be influenced by the IV
13. Independent Variables
The variables that are manipulated by the
experimenter
Each IV must have at least two levels
Remember the point of an experiment is
comparison
Combination of all the levels of all of the Ivs
results in the different conditions in an
experiment
14. Choosing your independent variable
Methods of manipulation
Straightforward manipulations
Stimulus manipulation - different conditions use different
stimuli
Instructional manipulation – different groups are given
different instructions
Staged manipulations
Event manipulation – manipulate characteristics of the
stimuli, context, etc.
Subject manipulations – there are (pre-existing mostly)
differences between the subjects in the different conditions
15. DependentVariables
The variables that are measured by the
experimenter
They are “dependent” on the independent
variables (if there is a relationship between the
IV and DV as the hypothesis predicts).
16. Choosing your dependent variable
How to measure your your construct:
Can the participant provide self-report?
Introspection – specially trained observers of their own thought
processes, method fell out of favor in early 1900’s
Rating scales – strongly agree-agree-undecided-disagree-strongly
disagree
Is the dependent variable directly observable?
Choice/decision (sometimes timed)
Is the dependent variable indirectly observable?
Physiological measures (e.g. GSR, heart rate)
Behavioral measures (e.g. speed, accuracy)
17. Choosing your dependent variable
Conceptual level: Memory
Operational level: Some kind of memory test
Memorize a list of words while eating the
candy
Then 1 hour after study time, recall the list of
words
Measure the accuracy of recall
19. Extraneous Variables
Random variables – may freely vary, to spread
variability equally across all experimental conditions
Randomization
A procedures that assure that each level of an extraneous variable
has an equal chance of occurring in all conditions of observation.
On average, the extraneous variable is not confounded with our
manipulated variable.
20. Control your extraneous variable(s)
Can you keep them constant?
Should you make them random variables?
Two things to watch out for:
Experimenter bias (expectancy effects)
the experimenter may influence the results (intentionally and
unintentionally)
E.g., Clever Hans
One solution is to keep the experimenter “blind” as to what
conditions are being tested
Demand characteristics – cues that allow the participants to
figure out what the experiment is about, influencing how they
behave
21. Confound Variables
Confound variables
Other variables, that haven’t been accounted for
(manipulated, measured, randomized, controlled) that
can impact changes in the dependent variable(s)
22. In experimental designs
Manipulate the IV in order to answer the question
Arrange the experiment so that extraneous variables
are controlled
23. In descriptive designs
Select the variables for observation in order to answer
the question
make the observations in a systematic and unobtrusive
manner so that the criterion variables are not
confounded by the extraneous variables
24. Control and Variability
Control is a restriction of natural variation
represent opposite extremes of ORDER and
DISORDER
both are essential to research
IV is controlled variation
25. Controlled Variables in Human
Communication Research
Subject (participant) variables
characteristics of subjects
Situation variables
characteristics of the situation in which the observations
are made
26. Control of Subject Variables
The type of communication disorder to be studied
is controlled by the selection of subjects who have
that type of disorder
Subject variables (e.g., age, gender, history of tx,
severity) are controlled by holding them constant
If these variables were not controlled, the effects of
the disorder might be confounded by the effects of
the uncontrolled variables
27. Control of Situation Variables
The research design also controls the situation
variables
These include variables such as time of day and
instructions given to subjects
The need for situational controls varies with the
type of design
EX: If you’re interested in determining how
sounds are detected in real-life situations,
you will not control background noise.
28. Control of Extraneous Variables:
Homogeneity
The control of extraneous variables means that the
influences of those independent variables extraneous to the
purposes of the study are minimized, nullified, or isolated.
There are four ways to control extraneous variables.
The principle of the first way is: To eliminate the effect of a
possible influential independent variable on a dependent
variable, chose participants so that they are as
homogeneous as possible on that independent variable.
29. Control of Extraneous Variables:
Randomization
The second way to control extraneous variance is
through randomization. Theoretically, randomization
is the only method for controlling all possible
extraneous variables. Another way to phrase it is: if
proper randomization has been accomplished, then
the experimental groups can be considered statistically
equal in all possible ways.
30. Control of Extraneous Variables:
Design
The third method of controlling an extraneous
variable is to build it right into the design as an
independent variable.
Unless one were interested in the actual difference
between the genders on the dependent variable or
wanted to study the interaction between one or two of
the other variables and gender, however, it is unlikely
that this form of control would be used.
31. Control of Extraneous Variables:
Matching
The fourth way to control extraneous variance is to match
participants.
The variable on which the participants are matched must
be substantially related to the dependent variable or the
matching is a waster of time.
If the same participants are used with different
experimental treatments—called repeated measures or
randomized blocked design—we have powerful control of
variance.
32. Control of Extraneous Variables
It should be forcefully emphasized that matching of
any kind is no substitute for randomization. If
participants are matched, they should then be
assigned to experimental groups at random.
If the same participants undergo all treatments, then
the order of the treatments should be assigned
randomly. This adds randomization control to the
matching, or repeated measures control.
33. Control of Extraneous Variables
When a matching variable is substantially correlated
with the dependent variable, matching as a form of
variance control can be profitable and desirable.
Before using matching, carefully weigh its advantages
and disadvantages in the particular research situation.
Complete randomization or the analysis of covariance
may be better methods of variance control.
34. Strategies for Gaining Control
Matching - narrow selection criteria (e.g., age, gender,
similarities in a particular condition) will limit
potential for error when comparing control vs.
experimental groups
Sampling method - a key factor in establishing control
Random assignment eliminates bias - makes groups as
comparable as possible
35. Strategies for Gaining Control
Double blind
Observer has no
knowledge of subject
group
Subject has no
knowledge of placebo
vs. treatment
Single blind
Subject has no
knowledge of
treatment vs. placebo
Blinding
Observer and/or
subject’s knowledge of
treatment may bias
outcomes
Blinding hides:
Observer’s knowledge of
subject assignment
(control vs. experimental)
Subject’s knowledge of
treatment (placebo vs.
experimental)
36. Strategies for Gaining Control
Placebo tends to make subjects feel they are receiving a
treatment or intervention being studied thereby
establishing control by eliminating potential bias
Caution: Deception by using a placebo may be
challenged by the IRB
37. Strategies for Gaining Control
Subjects as their own control
Subjects are matched to themselves
Exposed to all levels of independent variables
Control treatment or condition
Experimental treatment of condition
Inherently a repeated measures design
38. Strategies for Gaining Control
Analysis of covariance (ANCOVA)
A traditional way to statistically gain control
Partitions extraneous confounding variables
Treated as a covariate
Controls for initial differences between groups
Effect is to adjust scores on the dependent variable for pretest
differences between groups
Statistically establishes equivalence
39. Example - Covariate
Mean pretest measures
between groups are
likely to be different
Older subject’s soft
tissues often become
less elastic with age
Treat subject age as a
covariate
Measure maximal
hamstring length using a
“sit-and-reach” test in a
community-sponsored
fitness program before
and after a 10 weeks
exercise program
Groups
Children ages 8 - 16
Adults ages 30 - 50
