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Think of three experiments inspired by the classic Eames chair
DESIGN 1: EXPERIMENTSpurpose
problemsproof
Descriptive orientation Observation - Naturalistic - Field - no control
Relational Orientation Correlational, association - non-intervention - statistical control
Experimental Orientation Control and manipulation
DESIGNS
Descriptive orientation Observation - Naturalistic - Field - no control
Relational Orientation Correlational, association - non-intervention - statistical control
Experimental Orientation Control and manipulation
DESIGNS
WHY?
MANIPULATION &
CONTROL
WHY?
MANIPULATION &
CONTROLCAUSALITY
David Hume (1711 – 1776)Scottish Philosopher
conditions of causality
Must be evidence of1. Mutual relationship (covariation)2. Temporal precedence (one before the other)3. Rival explanations ruled out (internal validity)
We have to settle for best available evidence
Think of all the things that caused you to be in this room now?
John Stuart Mills (1806 –1873)English Philosopher
Logic of experiments
1. Method of agreement (if X, then Y)2. Method of difference (if not X, then not Y)
John Stuart Mills (1806 –1873)English Philosopher
Logic of experiments
1. Method of agreement (if X, then Y) Experimental Group2. Method of difference (if not X, then not Y) Control Group
RANDOMselectionallocation
How would you know if exercise reduced depression?
Designs
BETW EEN
BETW EENWITHIN
• Do males and females differ in their anxiety levels?• Does therapy reduce depression?• Does playing violent games lead to violent behaviour?• Is procrastination worse for males or females?• Does the university you attend affect your life chances?• Are richer people happier?• Does gardening improve concentration?• Does this lecture influence mood?• Does listening to music improve attention?
Within or Between?
BE TW EENBE TW EEN
FACTORIAL
3x3 BETWEEN
BE TW EENWI TH IN
FACTORIAL
3x3 mixed
MIXED
BET WEENBE TW EEN
FACTORIAL
2x3 BETWEEN
BET WEENBET WEENBET WEEN
FACTORIAL
2x2x2 BETWEEN
WI TH IN WI TH IN
FACTORIAL
3x3 WITHIN
WIT HIN WI TH IN
FACTORIAL
2x3 WITHIN
WIT HIN WIT HIN
FACTORIAL
2x2 WITHIN
BET WEENWIT HIN
FACTORIAL
2x2 MIXED
MIXED
BET WEENWI TH IN
FACTORIAL
2x3 MIXED
MIXED
And so on....
But... How many participants?Counterbalance within designsStatistical procedures....shhh later
Pre-Treatment End of treatment 6 months post treatment
CBT
Psychotherapy
Exercise
Control
Does therapy work – if so which works best?
How would this be written up?A 2 (time: pre vs post) x 4 (treatment: CBT, Psychotherapy, Exercise, Control) mixed factorial design, with repeated measures on the time variable.
What effects?Effect of TimeEffect of ConditionInteraction of Time and Condition
counterbalancing
“Help, my experiments got problems...”
Internal Validity
Threats
History = If study over time, what else has happened in the mean time?Maturation = If study over time, what has happened to the participants?Instrumentation = Are the instruments valid?Selection = Has this had an effect?Attrition = Have people dropped out? Some more than others?
Can we be sure that the effect is due to the variables we thought?
ExternalValidityTask = is it ecologically valid?Setting = are the findings limited to a setting?Time = when was the study conducted, could this matter?Participants = can we generalise from them?
Threats
Can we extrapolate from the study itself?
The psychology of the experiment
What the @*!#?
SYSTEMATICRANDOM
Artifacts
ERRORS
SYSTEMATICRANDOM ERRORS
“Did I do ok?”“Did I ruin the study?”“Did I do it right?”
“Did I do ok?”“Did I ruin the study?”“Did I do it right?”
“How should I behave here?”“Did I perform well in my rôle as an experimental subject”
Demand Characteristics
Volunteering is a commitment to comply!
Don’t ask WHY, just ask WHERE?
SYSTEMATICRANDOM
Artifacts
ERRORSGood subjectsEvaluation apprehension – look goodExperimenter effects
Situations– novel, formal, public– detailed and complete instructions– little choice of behaviour– brief duration
Personality– familiar, informal, private– few or no instructions– considerable choice of behaviour– lasts for a long time
When do situations matter?
Buss, A.(1989) Personality As Traits. American Psychologist, 44, 1378-1388
Like experiments Less like experiments
Let’s have a look at doing some analysis
Pre-Treatment End of treatment 6 months post treatment
CBT
Psychotherapy
Exercise
Control
Does therapy work – if so which works best?
How would this be written up?A 2 (time: pre vs post) x 4 (treatment: CBT, Psychotherapy, Exercise, Control) mixed factorial design, with repeated measures on the time variable.
What effects?Effect of TimeEffect of ConditionInteraction of Time and Condition
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