review during the last lecture we were discussing the use of experiments as a way of answering...
TRANSCRIPT
Review
• During the last lecture we were discussing the use of experiments as a way of answering questions about the causal relationship between variables
• If we can systematically manipulate a variable and show that it has an effect on another variable, then we have a strong basis for concluding that one variable affects the other.
Experimental Research
• Between- and within-subjects designsbetween-subjects: different people are exposed to each level
of the IV
within-subjects: the same people exposed to each level of the IV
• Mixed design: one factor is a between-subjects factor and the other is a within-subjects factor
Pros and cons of different designs
Between Within
Pros (a) Minimize reactance effects (a) Requires fewer research subjects
Cons (a) Requires more research subjects
(b) The people in the two conditions may vary for reasons that have nothing to do with your manipulation.
(a) Awareness of different levels of independent variable
(b) Learning & practice effects
Counter-balancing
t1 t2 t3
Person 1 C1 C2 C3
Person 2 C1 C3 C2
Person 3 C2 C1 C3
Person 4 C2 C3 C1
Person 5 C3 C1 C2
Person 6 C3 C2 C1
Counter-balancing helps to ensure that the specific test Conditions used (C1, C2, C3) are uncorrelated with order of presentation
Factorial Designs
• Today we’re going to discuss experimental designs involving more than one independent variable.
• Why might we want to manipulate more than one variable in an experiment?– to study multiple variables at once– we may have reason to believe that the effects of one
variable on another are conditional upon a third variable. Example: It may be the case that whether or not people behave aggressively after viewing violent television depends on whether they’ve been provoked or threatened.
Factorial Designs
• Multiple independent variables• Factorial designs
[# of levels] [# of levels]
IV#1 IV#2
Example: a 2 3 factorial design2 levels of the first IV, “violent TV viewing” (e.g., watching
violent TV and nonviolent TV) and 3 levels of second IV, “provocation” (e.g., 0 threats, 1 threat, 2 threats)
Factorial Designs
• Possible outcomes in a 2 2 designmain effect: manipulating one of the IV’s produces a change in
the DV
in a 2 2 design, you can have 0, 1, or 2 main effects
interaction: the effect of one IV on the DV is dependent on the other IV
0
5
10
15
20
25
A1 A2
B1
B2
No main effect of A or B, no interaction
Aggressive TV viewing
Provocations A1 A2
B1 20 20 20
B2 20 20 20
20 20
Viewing Aggressive TV
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
This represents a situation in which the experimental manipulations have no effects on the dependent variable.
Main effect of A, no main effect of B and no interaction
Aggressive TV viewing
Provocations A1 A2
B1 20 40 30
B2 20 40 30
20 40
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Watching violent TV leads to increases in aggressive behavior.
Main effect of B, no main effect of A and no interactions
Aggressive TV viewing
Provocations A1 A2
B1 20 20 20
B2 40 40 40
30 30
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Being provoked leads to increases in aggressive behavior.
Main effect of A and B, no interaction
Aggressive TV viewing
Provocations A1 A2
B1 0 20 10
B2 20 40 30
10 30
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Watching violent TV leads to aggressive behavior.
and
Being provoked leads to increases in aggressive behavior.
No main effect of A or B; interaction
Aggressive TV viewing
Provocations A1 A2
B1 40 20 30
B2 20 40 30
30 30
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Whether people behave aggressively after watching violent TV depends on whether they’ve been provoked.
If provoked, violent TV leads people to behave aggressively.
If not provoked, violent TV leads people to behave less aggressively.
Main effect of A, no main effect of B; interaction
Aggressive TV viewing
Provocations A1 A2
B1 40 0 20
B2 20 20 20
30 10
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Watching violent TV leads to less aggressive behavior.
and
it depends. Watching violent TV leads people to behave less aggressively when they have not been provoked.
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Main effect of B, no main effect of A; interaction
Aggressive TV viewing
Provocations A1 A2
B1 20 0 10
B2 20 40 30
20 20
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Being provoked leads to more aggressive behavior.
and
it depends. Being provoked leads to more aggressive behavior when watching violent TV. When not watching violent TV, provoked and non-provoked people are equally aggressive.
0
5
10
15
20
25
30
35
40
45
A1 A2
B1
B2
Main effect of A and B; interaction
Aggressive TV viewing
Provocations A1 A2
B1 20 20 20
B2 20 40 30
20 30
Aggressive TV viewing
Ag
gre
ssiv
e b
ehav
ior
(DV
)
Provocations
Watching violent TV leads to more aggressive behavior.
and
Being provoked leads to increases in aggressive behavior.
and
it depends. In the absence of provocation, there is no effect of violent TV viewing on behavior. When provoked, watching violent TV leads people to behave more aggressively.