Research Methods in Psychology – Statistics & Experimental
Design Review
Research methods in psychology focus on how psychologists design studies, collect data,
analyze findings, and draw conclusions scientifically. Major areas include experimental
design, sampling, validity and reliability, and statistics.
1. Experimental Design
Types of Experiments
Type Description Advantage Limitation
Laboratory Experiment Conducted in controlled environment High control
Low realism
Field Experiment Conducted in natural setting More realistic Less control
Natural Experiment IV occurs naturally Useful when manipulation impossible
Low control
Quasi-Experiment Participants already belong to groups Practical No random
assignment
Example
A psychologist testing whether sleep affects memory may:
Manipulate sleep hours (IV)
,Measure memory score (DV)
2. Variables
Independent Variable (IV)
The factor manipulated by the researcher.
Dependent Variable (DV)
The measured outcome.
Extraneous Variables
Variables that may influence results unintentionally.
Confounding Variables
Variables that change alongside the IV and threaten validity.
3. Experimental Designs
,Design Description Strength Weakness
Independent Groups Different participants in each condition No order effects
Participant differences
Repeated Measures Same participants in all conditions Fewer participant variables
Order effects
Matched Pairs Participants matched on characteristics Reduces differences Time-
consuming
4. Hypotheses
Null Hypothesis (H₀)
Predicts no significant effect or relationship.
Alternative Hypothesis (H₁)
Predicts a significant effect or relationship.
Directional vs Non-Directional
Directional: predicts direction
Non-directional: predicts difference only
, Example:
Directional: “Students who sleep more will score higher.”
Non-directional: “There will be a difference in scores.”
5. Sampling Methods
Sampling Method Description
Random Sampling Equal chance for all
Opportunity Sampling Easily available participants
Volunteer Sampling Participants volunteer
Stratified Sampling Sample reflects population proportions
Systematic Sampling Every nth participant selected
6. Reliability and Validity
Reliability
Design Review
Research methods in psychology focus on how psychologists design studies, collect data,
analyze findings, and draw conclusions scientifically. Major areas include experimental
design, sampling, validity and reliability, and statistics.
1. Experimental Design
Types of Experiments
Type Description Advantage Limitation
Laboratory Experiment Conducted in controlled environment High control
Low realism
Field Experiment Conducted in natural setting More realistic Less control
Natural Experiment IV occurs naturally Useful when manipulation impossible
Low control
Quasi-Experiment Participants already belong to groups Practical No random
assignment
Example
A psychologist testing whether sleep affects memory may:
Manipulate sleep hours (IV)
,Measure memory score (DV)
2. Variables
Independent Variable (IV)
The factor manipulated by the researcher.
Dependent Variable (DV)
The measured outcome.
Extraneous Variables
Variables that may influence results unintentionally.
Confounding Variables
Variables that change alongside the IV and threaten validity.
3. Experimental Designs
,Design Description Strength Weakness
Independent Groups Different participants in each condition No order effects
Participant differences
Repeated Measures Same participants in all conditions Fewer participant variables
Order effects
Matched Pairs Participants matched on characteristics Reduces differences Time-
consuming
4. Hypotheses
Null Hypothesis (H₀)
Predicts no significant effect or relationship.
Alternative Hypothesis (H₁)
Predicts a significant effect or relationship.
Directional vs Non-Directional
Directional: predicts direction
Non-directional: predicts difference only
, Example:
Directional: “Students who sleep more will score higher.”
Non-directional: “There will be a difference in scores.”
5. Sampling Methods
Sampling Method Description
Random Sampling Equal chance for all
Opportunity Sampling Easily available participants
Volunteer Sampling Participants volunteer
Stratified Sampling Sample reflects population proportions
Systematic Sampling Every nth participant selected
6. Reliability and Validity
Reliability
