1. Lecture 8 Complex Experimental Designs
PSY2004 Research Methods & Ethics in Psychology PSY2005 Applied Psychology Research Methods & Ethics

2. Experimental Designs Experiments Quasi-Experiments
Characterised by random assignment of groups or participants to conditions.
At least one variable is manipulated by the experimenter(s).
Usually employs a control group
Experiments
Groups or subjects not randomly assigned (e.g., sample of convenience)
May not have a comparison group
Quasi-Experiments

3. The Principle of Analysis Of VAriance (ANOVA)
Total Variability
Systematic
Variance (caused by IVs and found in differences between means
Unsystematic variance (caused by things we do not know about)

4. Independent Variables
Types of Variable
what is manipulated in the experiment
Independent Variables
what is measured
Dependent Variables
what is held constant
Control Variables
what is allowed to vary randomly
Random Variables
correlated with an independent variable
Confounding variable

5. Design Terminology Between Groups Repeated Measures Mixed
An “independent groups” design
Different groups
Dependent measures taken one time
Between Groups
A “within groups” design
One group, different conditions
Dependent measures taken multiple times
Repeated Measures
Between and repeated
Mixed

6. Single factor (one-way)
Design Complexity
Studies one independent variable
Single factor (one-way)
Studies multiple independent variables
May have several levels
Examples:
Two-way (e.g., 2 x 2)
Three-way (e.g., 2 x 2 x 2)
Factorial

7. Factorial Design
Two or more independent variables are studied in order to determine their independent and interactive effects on the dependent variable.

8. Unsystematic variance (caused by things we do not know about)
The Principle of Analysis Of VAriance (ANOVA: mood by intelligence example)
Total Variability
Systematic
Variance
mood
intelligence
Interaction
Unsystematic variance (caused by things we do not know about)

9. Main Effect
Two or more independent variables are studied in order to determine their independent effects on the dependent variable.

10. Example Main Effect of Intelligence on Creativity
Conclusion: people that are high in IQ score higher on creativity
Tests regardless of mood. No effect for mood

11. Interaction Effect
The effect of one factor (independent variable) depends on the level of the other factor (other independent variable).

12. Main Effects & Interactions
High
High
Sadness
Sadness
High
High
Low
Low
Important point is that whenever both main effects and interaction effects are significant, only the interaction effect is interpreted since interaction effect modify the meaning of the main effect if it were to be interpreted on its own.
Lightness
Lightness
Seasonal Affective Disorder
No Seasonal Affective Disorder

13. A Detailed Example Godden and Baddeley (1975) Memory Context Study
Participants (who were divers) learned lists of words either on the beach, or beneath 15 feet of water and then recall in the same or opposite environment.
2 IVs:
Place of learning (2 levels: Beach or Underwater)
Place of recall (2 levels: Beach or Underwater)
DV: Number of words recalled

14. A Detailed Example Four Conditions: Learn on Beach Recall on Beach
Learn Underwater
Recall Underwater
Recall on Beach

15. A Detailed Example

16. Advantages of Factorial Designs
More than one hypothesis can be tested.
Potentially confounding variables can be built into the design as factors.
Enables interaction effects to be tested.

17. Randomised Controlled Trials
An experimental design used to evaluate the effectiveness of psychological interventions. Participants assigned randomly, to one of at least two conditions
Pre & post tests
Outcomes measured before & after intervention
Control group
Includes no treatment; treatment as usual; and ‘wait list’ sample.

18. Example Does Psychological Therapy improve outcomes
for People with Mild/Moderate Depression?
Psychological Therapy
(CBT + TAU)
Sample
Ramdomise
Treatment as Usual TAU
2 IVs: 1) Time of measurement (pre- or post)
2) Treatment Group (CBT or TAU)
DV: Self-reported mood/symptoms

19. Results of Study Main effect of Time? Yes
Main effect of type of treatment? Possibly but not important
Interaction between time and type of treatment? Yes
Simple main effects?
Conclusion: These results show a significant interaction between time
and intervention. Whilst the participants reported lower depression following
Treatment this effect was stronger in the CBT Treatment

20. Complex Designs 1
Complex designs represent research which has more than one independent variable.
Complex designs have more than one outcome: main effects and interaction effects
Example complex designs
Two independent groups IVs and one DV
Place of learning (beach/underwater): Main effect 1
Place of recall (beach/underwater): Main effect 2
Learning by recall: interaction effect
DV: memory recall

21. Complex Designs 2: Independent Groups
A independent groups designs is one in which the participant is in a single level of one IV.
The role of attraction and type of crime in determining prison sentence
IV1: Attraction: Attractive/Ordinary
IV2: Type of Crime: Robbery/Swindle
DV: Time spent in jail

22. The role of type of crime and attraction on determining prison sentence
ME Attraction: NS
ME Type of Crime: Swindle > Robbery
A x TofC: Significant cross-over effect
Conclusion: Although attractive people are likely to be given lenient sentences, when they use their attractiveness to commit a crime they are given longer sentences.

23. Complex Designs 2: Repeated Measures Design
A repeated measures designs in which the participant takes part in all of the conditions in the experiment
Can mood effect performance on visual and verbal forms of creativity
Mood (positive/negative)
Type of creativity (visual/verbal)
DV: creativity task performance

24. Results Type of Creative: main effect fully explained by interaction
Mood: main effect fully explained by interation
T x M: Significant effect that explains the systematic variance found
Conclusion: that people perform better on visual creativity tasks
When they are in a positive mood.

25. Complex Designs: The mixed model
A mixed model is one in which there is at least one independent groups IV and at least one repeated measures IV.
Example: The effects of sex differences on types of intelligence
Sex (male/female): IG variable
Intelligence (spatial/verbal): RM variable
Sex by type of intelligence: Interaction effect
Intelligence score: DV

26. Outcome for the mixed model
ME Intelligence: No effect
ME sex: No effect
I x S: Significant crossover effect
Conclusion: both within and between women are better at verbal tasks
and men are better at Spatial tasks