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Introduction to Psychology
Methods: Experiments
Prof. Jan Lauwereyns
http://www.sls.kyushu-u.ac.jp/~dubito/links
Look under “Classes”
Check “Psychology”
Rea
ctio
n T
ime
GREEN GREENXXXXX
Staged
-Deliberation time: how long do you get to look at the photos2s, 5s or Free
-Similarity: how similar are the photosSim (similar) or Dis (dissimilar)
-Deliberation time: how long do you get to look at the photos2s, 5s or Free
-Similarity: how similar are the photosSim (similar) or Dis (dissimilar)
-Deliberation time: how long do you get to look at the photos2s, 5s or Free
-Similarity: how similar are the photosSim (similar) or Dis (dissimilar)
-Deliberation time: how long do you get to look at the photos2s, 5s or Free
-Similarity: how similar are the photosSim (similar) or Dis (dissimilar)
Fre
qu
en
cy d
istr
ibu
tion
of
typ
es o
f re
sp
on
ses
Experimental & Nonexperimental
• Experimental: – Direct manipulation and control of
variables– Manipulate variable of interest & record
results
• Nonexperimental:– Observations of phenomena as they
occur naturally
Choosing a Method
• Ethical and practical considerations• Artificiality of experiments
– Field experiments?
• Participant variables• Description of behavior• Successful predictions of future
behavior• Advantages of multiple methods
Evaluating a method
• Construct validity– Does the operational definition reflect the
true theoretical meaning of the variable?
• Internal validity– Can you draw strong conclusions about
causal relationships from the data?
• External validity– To what extent can results be generalized?
Experimental method
• Experimental control– Keep all factors under control (…)- Avoid that results are influenced by
extraneous variables (confound)
• Randomization– Hope that your systematic
measurements are not affected by other, randomized variables
Experimental Methods
• Independent variableIndependent variable (IV) variable manipulated by the experimenter
• Dependent variableDependent variable (DV) variable measured by the experimenter
Measuring activity level of blood flow in fMRI scan
Female
Measuring activity level of blood flow in fMRI scan
Female
Male
Measuring activity level of blood flow in fMRI scan
Female
Male
Left brain Right brain
Generalization as a statistical interaction
• Say, a study was done with only males
• You question the generalizability• …that is, suggesting an
interaction
Em
path
y
a
s m
easu
red
in
b
rain
acti
vit
y level
Fair player Unfair player
women
Em
path
y
a
s m
easu
red
in
b
rain
acti
vit
y level
Fair player Unfair player
women
men
No interaction
Em
path
y
a
s m
easu
red
in
b
rain
acti
vit
y level
Fair player Unfair player
women
men
Interaction
Em
path
y
a
s m
easu
red
in
b
rain
acti
vit
y level
Fair player Unfair player
women
men
Interaction
M
ean
rati
ng
(
hig
h =
have h
on
ou
red
well)
Maori have honoured…
Pakehahave honoured…
How well have people honoured the Treaty of Waitangi?
Pakeha think…
M
ean
rati
ng
(
hig
h =
have h
on
ou
red
well)
Maori have honoured…
Pakehahave honoured…
Maori think…
Pakeha think…
How well have people honoured the Treaty of Waitangi?
