This document discusses different types of variables that can be studied in psychological research, including independent, dependent, extraneous, and confounding variables. It provides examples and describes how to conceptualize and operationally define variables. The key aspects of gaining control in an experiment are discussed, including controlling subject variables through matching or random assignment, controlling situation variables, and using strategies like blinding or placebos. Extraneous variables should be controlled through randomization, the design of the study, matching, or statistical techniques like analysis of covariance.

1. Dr. Tushar Singh

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

5. Examples
Variable Attribute
age

6. Examples
Variable Attribute
age 18, 19, 20, etc...

7. Examples
Variable Attribute
Gender or sex

8. Examples
Variable Attribute
Gender or sex Male, female

9. Examples
Variable Attribute
satisfaction

10. Examples
Variable Attribute
satisfaction 1 = very satisfied
2 = satisfied
3= somewhat satisfied
4 = not satisfied
5 = not satisfied at all

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

12. Examples
IV DV
exercise
participation
health status
attitude
social support
intervention

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

18. Extraneous Variables
 Control variables
 Holding things constant - Controls for excessive random
variability

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