1. CHAPTER 6 Control Problems in Experimental Research

2. Between-Subjects Designs
Comparison is between two different groups of subjects (each subject receives one level of IV)
Necessary when
Subjects in each condition have to be naïve (example: Barbara Helm study (type of crime and attractiveness))
Subject variable (e.g., gender) is the IV
Main problem to solve: creating equivalent groups
Level 1
Level 2

3. Creating Equivalent Groups
Random assignment
Each subject has equal chance of being assigned to any group in the study
Spreads potential confounds equally through all groups
Accomplished through blocked random assignment

5. Creating Equivalent Groups
Random assignment
Each subject has equal chance of being assigned to any group in the study
Spreads potential confounds equally through all groups
Accomplished through blocked random assignment
Matching
Deliberate control over a potential confound
Use when
Small N per group might foil random assignment
Some matching variable correlates with DV
Measuring the matching variable is feasible

6. Within-Subjects Designs
Also called repeated-measures designs (same subjects in every level of an IV)
Comparison is within the same group of subjects
Used when comparisons within the same individual are essential (e.g., perception studies)
Removes possibility that differences between levels of the IV due to individual differences
Level 1
Level 2

7. Within-Subjects Designs
Main problem to solve  order effects
Practice effect (progressive)
Carry-over (harder to control)
Sequence A-B may yield differ carryover than the sequence B-A

8. Controlling Order Effects
RGB
RBG
BGR
BRG
GRB
GBR
Counterbalancing
Altering the order of the experimental conditions
Complete counterbalancing (all possible orders = x!)
Test participants in every possible different order at least once
Works well with only a few conditions
Partial counterbalancing
Random sample of all possible combinations is selected
RGBY
RGYB
RYGB
RYBG
RBGY
RBYG
GRBY
GRYB
GBYR
GBRY
GYBR
GYRB
BYRG
BYGR
BRYG
BRGY
BGYR
BGRY
YGBR
YGRB
YRBG
YRGB
YBRG
YBGR

9. Methodological Control in Developmental Research
Cross-sectional design
Longitudinal design
Cohort sequential design

10. Cross-sectional design
Methodological Control in Developmental Research: Cross-Sectional Design
Cross-sectional design
Between-subjects design
Participants are arranged in age cohorts
Potential for cohort effects
Cohort effect: the impact on a study of a group of individuals bonded by age or common experiences
Worse with large age differences

11. Methodological Control in Developmental Research: Longitudinal Design
Within-subjects design
Participants are re-measured over long spans of time
Expensive, time-consuming, likelihood of attrition high
In this case, we’d be measuring texting behavior every ten years from when our group is aged 10 all the way to when the same group is aged 80

12. Cohort-sequential design
Methodological Control in Developmental Research: Cohort-sequential Design
Cohort-sequential design
Both within- and between- subjects design
Measure texting of one group at age 60 and 80
Measure texting of a different group at age 40 and 60
Measure texting of a different group at age 20 and 40

13. Problems with Biasing Experimenter bias/Experimenter Expectancy bias
Experimenter expectations can influence subject behavior
Controlling for experimenter bias
Automating the procedure
Using a double blind procedure

14. Problems with Biasing Subject/Participant bias
Hawthorne effect: Effect of knowing one is in a study
Evaluation apprehension
Participants tend to behave in ideal ways so as not to be evaluated negatively
Demand characteristics
Cues giving away true purpose and study’s hypothesis
Controlling for participant bias
Effective deception
Field research

15. Ethical Responsibilities of Participants
Be responsible
Show up for scheduled appointments, or inform research of cancellation
Be cooperative
Behave professionally when participating in research
Listen carefully
Ask questions if unsure of your rights or of what you are asked to do
Respect the researcher
Do not discuss study with others
Be actively involved in debriefing
Help the researcher understand your experience