3. Contrast
Generally contrast is observed commonly b/w
Several Levels of IVs on Group of Subjects
Experimental Group: receives the treatment
(levels of IVs)
Control Group: do not receive the treatment
4. Scientific Inferences
Scientific theories are based on
inferences
Human behaviors and thoughts changes
under a variety of conditions
Experimental Psychologist observe the
behavior caused by some variable
Develop models – generalization –
development of the laws
5. Basis of the validity of the observation
Influence of the Independent Variables
Characteristics of the subjects
Importance of Experimental and Control
Groups are similar as possible
Lack of control – results may be meaningless
or miss leading
Techniques have evolved to safeguard the
errors due to lack of control
6. Types of Control
Independent Variable
Control IV to see effects on DV
Determine the kind and quantity of the
variable
Hold conditions Constant
Only IV should be manipulated rest of the
variables to be held constant
Various treatment groups and control
groups must be treated alike (except for
the manipulation of IV)
7. So the change in DV will be only b/c of IV
The variables other than IV effects the DV are
Extraneous and Confounding Variables
The experimenter is not sure either the
change is due to IV or due to Extraneous
variable or due to both
Inclusive results
Repeat the research and eliminate them
8. What makes a variable
extraneous???
Depends on DV
Varies from experiment to experiment
One variable might be extraneous for one
experiment but might not be for other
Control only those variables which could
effect the DV
Sound judgment and Knowledge can improve
experimental design
9. Controlling Extraneous Variables
Manipulate IV in different treatment groups
Hold Conditions Constant (control and
experimental groups)
10. Holding Conditions Constant
Lorge (1930) experiment; massed vs
distributed practice
IV= length of time b/w practice session
(interval)
Constant Variables
Same task
Same amount of practice
Task related abilities
11. By ensuring that these variables were
the same for all treatment groups-
eliminated them as explanation of the
results
Basic logic behind keeping the variables
constant
12. Subject Variables
Good Experimental Design – Holding
Conditions Constant
Some times violation may occur
Not possible to construct the checklist of all
the extraneous variables
Problematic areas
IV is a subject variable – hence all the
other subject variables may also effect
13. Experimental results may be due to other
subject variables – Subject Variable or
Subject Variable Confound
Potentially erroneous results which may be
attributing to secondary causes based on
confounding or joining subject variables
Example?????
Authoritarian people – would have difficulty
in learning complex material than non-
authoritarian people
High-Authoritarian People think in a
simplistic manner- difficulty in learning
14. Low-authoritarian people recalled better
than High-authoritarian people
Criticism- inverse relationship b/w
authoritarianism and intelligence
Learning is effected b/c of intelligence
Subject variable is not being
manipulated- subject variable confound
to little danger
15. Experimental Paradigm
A paradigm in experimental psychology is
a model or pattern an investigator uses to
organize research
Independent Subject Design
Matched Subject Design
Repeated Measure Design
Repeated measure Design with
Sequence Counterbalance
Factorial Design
16. Wine-Testing Experiment
Effect of color on the enjoyment of the person
IV= Color
DV= Rating (Lickert Scale 1-5)
1 2 3 4 5
Absolutely Not
Enjoyable
Not
Enjoyable
Moderatel
y
Enjoyable
Enjoyabl
e
Absolutely
Enjoyable
18. Independent Subject Design
Independent Subject Design or B/W-Group
Design-
Group I - artificially colored wine (called???)
Group II – natural colored wine (called ???)
Subject in one group are independent from
other group
Sample: 16 uni students (ages 21-30)
8 participants per group
19. Minimum for this kind of sample 8 each
Randomized Subject Design
Model 1. Independent Subject Design
Experimental Group
(Artificial Colored Vine)
Control Group
(Natural Colored Vine)
S1 1 S9 5
S2 2 S10 4
S3 2 S11 3
S4 1 S12 5
S5 2 S13 5
S6 1 S14 4
S7 1 S15 4
S8 4 S16 5
20. Analyze the means (average) through t-
test- mathematical precision
Statistical Significance
Highly unlikely chances of huge
differences
Draw inferences
Paradigm is common in Psychological
Experiments
Subject variables distributed among the
groups on the basis of random
distribution
21. Matched Subjects Designs
Some variable may be critical to effect the
DV
So the participants should be matched on
that variable
Wine-testing Experience –better sensory
discrimination
Sex, age, intelligence, running ability or
training
22. Model 2. Matched Subject Design
Experimental Group
(Artificial Colored Vine)
Control Group
(Natural Colored Vine)
S1 a 3 S9a 5
S2b 2 S10b 4
S3c 2 S11c 4
S4d 3 S12d 5
S5e 2 S13e 5
S6f 3 S14f 4
S7g 3 S15g 4
S8h 4 S16h 5
23. Powerful Design: matched variable is related
to DV
Also relate to IV on which the matching
variables are made
Invalid test or measure for the characteristics
spoils the basic assumption
Correlated t-test or Dependent t-test
24. Repeated Measure Design
With-in Subject Design
Subjects being exposed to two or more
conditions
Taste both kinds of Wine
Each subject will be his or her own control
Gathers more data
Limited subjects can be a limitation
26. Repeated Measure Design
Counter Balance the Sequence
Sequence is important
Half of the participants will balance the
colored wine first and half will natural colored
wine first
Multiple repeated designs
Specialized statistical analysis
27. Model 4. Repeated Measure Design
Experimental
Group
(Artificial
Colored Vine)
Control Group
(Natural
Colored Vine)
S1 S9
S2 S10
S3 S11
S4 S12
S5 S13
S6 S14
S7 S15
S8 S16
Experimental
Group
(Artificial
Colored Vine)
Control Group
(Natural
Colored Vine)
S9 S1
S10 S2
S11 S3
S12 S4
S13 S5
S14 S6
S15 S7
S16 S8
28. Factorial Designs
Effect of Multiple IVs on a DV
Not specifically constructed subject variable
Possible Method for within subject design
Modify the example:
IV 1: Color of Wine (natural or burgundy)
IV 2: Type of Grapes (Zinfandel, Pinot Noir or
Chardonnay)
Factorial Design?????
29. Factorial Design: With-in Subject/
Repeated Measure
IV 1 Color of Wine
Natural Burgundy
IV 2 Type
of Grapes
Pinot Noir S1, S2, S3, S4 S1, S2, S3, S4
Zinfandel S1, S2, S3, S4 S1, S2, S3, S4
Pinot Noir S1, S2, S3, S4 S1, S2, S3, S4
30. Factorial Design: B/W Group
Design/Independent Subject Design
IV 1 Color of Wine
Natural Burgundy
IV 2 Type
of Grapes
Pinot Noir S1, S2, S3, S4 S13, S14, S15, S16
Zinfandel S5, S6, S7, S8 S17, S18, S19, S20
Pinot Noir S9, S10, S11, S12 S21, S22, S23, S24
31. Use of Treatment and Control
Group
What is Control Group????
A group of subjects similar to exp group i.e.
exposed to all the conditions of an
investigation except for the exp variable (IV)
Selection of Sample: Random from the
population for generalization (in majority of
the cases)
