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PSY 250
Chapter 7: Experimental Research Strategy
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Cause and Effect Relationships
Can be clear relationship but not a causal one – e.g. between getting dressed up and having a headache the next morning
4 basic elements to establish cause and effect:
1. Manipulation
2. Measurement
3. Comparison
4. Control
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Variables
Independent Dependent Extraneous
Levels of the IV The different values of the IV selected to create and
define the treatment conditions Must be ≥ 2
Treatment Condition Situation or environment characterized by one specific
value of the IV
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The Third-Variable Problem
Can be clear relationship but not a direct causal one between 2 variables E.g. children’s involvement in extra-curricular
abilities and confidence 3rd variable may be controlling both of the
other 2 (family involvement, opportunities for more friendships)
Research becomes the art of teasing apart and separating a set of naturally interconnected variables
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Control
Eliminate all confounding variables E.g. Meaningfulness and imagery (Paivio,
1965) Create two lists (high vs. low imagery) with
equal average meaningfulness
Classification of confounding vs. independent variable depends on research hypothesis
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The Directionality Problem
Which is the cause and which is the effect E.g. assertiveness and success Sleep and depression
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Manipulation and Control
Unique to experimental research strategy
Manipulation Create treatment conditions corresponding to
values of IV
If change in A does not cause change in B then A is not a causal agent (unless change is too small to affect B)
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Control
Prevent extraneous variables from becoming confounding variables
Only confounding if it influences DV
AND It varies systematically with IV 3 types of extraneous variables:
Environmental Participant Time - Related
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Methods of Controlling Extraneous Variables
1. Holding a Variable Constant Hold absolutely constant or Limit to restricted range
But can limit generalizability What is this a threat to?
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Methods of Controlling Extraneous Variables 2. Matching Values across Treatment
Conditions E.g. each condition has = males and females Or ensure average value is same – e.g.
average age is 4.5 in each group Also match on environmental and time
variables
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3. Matching by Yoked Control
Controls for possible influence of temporal relationship between event and response
Ulcers due to physical or psychological stress of shock in monkeys (Brady, 1958)
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4. Building Extraneous Variable into the Design
Sample of participants with IQs of 90 - 119
Subsamples with specified IQ values identified
Participantswith 90-99 IQ
Participantswith 100-109 IQ
Participantswith 110-119 IQ
IQ values
built into design
Learning strategy
A
B
90 - 99 100 -109 110 -119
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5. Matching by Equating Participants
Also increases sensitivity of exp. Similar to building EV into design # of participants is some multiple of the # of
levels of the IV Two methods
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5a. Precision Control
Sample of research participants
Each participant measured interms of age, gender, IQ, etc
Each participant matchedwith 2nd participant of same age, gender, IQ, etc.
Provides many matched pairs of participants
Each pair of matched participants randomly assigned to the treatment conditions
Treatment A Treatment B
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5b. Frequency Distribution Control
0
20
40
60
80
100
0
20
40
60
80
100
1st sample of participants
Mean = 107 S.D. = 5.4
2nd sample of participants
Mean = 106.5 S.D. = 5.1
Similar frequency distribution of IQ scores
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Methods of Controlling Extraneous Variables 6. Randomization
Disrupts any systematic relation between EVs and IV – prevents EVs from becoming CVs
Unpredictable, unbiased procedure to distribute different values of each EV across treatment conditions
All possible outcomes equally likely But chance CAN produce biased outcomes –
e.g. all heads with 10 coin tosses
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Control Through Participant Assignment
Random assignment ensures influential extraneous variables
are balanced among experimental conditions
“whenever possible, randomize” representative
Free random assignment random numbers
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Counterbalancing
To control for sequencing effects Order effects
IV – rate of presentation of nonsense syllables DV – verbal learning Learn slow, moderate then fast list – speed
confounded with order Carry-over effects
Performance in condition partially dependent on preceding conditions
IV – monetary reward Dime may be more rewarding when preceded by 5 vs.
15 cents
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Control Groups
No treatment condition Provides baseline measure of normal behavior
Experimental group – treatment condition
Placebo control groups
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General Control Procedures
Preparation of setting structuring research setting
Response measurement careful selection and preparation of
measures Replication
systematic and conceptual replication
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Control Over Subject and Experimenter Effects
Experimenter effects Participant (subject) effects
demand characteristics
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Control Over Subject and Experimenter Effects (cont’d)
Single-blind procedures experimenter is unaware
Partial-blind Experimenter unaware for portions of
exp. Double-blind procedures
experimenter and participant are unaware
Deception Participant is unaware
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Control Over Experimenter Effects (cont’d)
Automation reduces experimenter-participant contact
Using objective measures require minimal judgements
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Control Over Subject and Experimenter Effects (cont’d)
Multiple observers ratings of behaviors
Control of experimenter attribute errors physical and psychological characteristics Hold constant across treatments
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Gaining Insight Into Participants’ Perceptions of Experiment
Experimental manipulation check Did manipulation work? What did participant think experiment was
about? How does participant think others will respond?
Participant Manipulations Subtle Manipulations Simulations Placebo Controls
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Simulation Studies
Try to duplicate natural environment in lab – bring real world into lab
Mundane Realism Superficial, physical characteristics
Experimental Realism Psychological aspects of situation Do participants become immersed in situation E.g. Haney, Banks & Zimbardo (1973)
prisoner study Prisoner’s dilemma
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Field Studies
Bring lab into real world E.g. Bystander Apathy in emergency
situations