MIDTERM 1 Flashcards
Describe the non experimental method
Both variables are measured and determined if they correlate
Why cannot causal statements be made from the non experimental method?
- No temporal precedence
- The third variable problem: extraneous variables may be causing the relationship
Types of non experimental relationships
- Positive linear
As one variable increases, so does the other - Negative linear
As one variable increases, the other decreases - Curvlinear
The direction of relationship changes at least once - No relationship
Circle scatter plot/horizontal line
What is an experimental method
Direct manipulation and controls of variables
Can describe a causal relationship between variables
Difference between an independent and dependent variable
Independent: manipulated
Dependent: measured
What is temporal precedence?
Causal variable comes first
How is causality established?
- Temporal precedence
- Covariation
- Eliminate plausible alternative explanations
Some also say the cause needs to be:
- Necessary
- Sufficient
Define Covariation
participants show a different effect between the control and experimental condition
How are alternative explanations eliminated?
- Use an experimental control
- Use random assignment so that any extraneous variables are just as likely to affect each group
How is high internal validity met?
When only the independent variable can be the cause of the results
- Temporal precedence, covariation and eliminating alternative explanations
Difference between necessary and sufficient?
Necessary: cause must be present for the effect to occur
Sufficient: cause will always produce the effect
Experimental design steps
- obtaining equivalent groups of participants
- Introducing the independent variable
- Measuring the effects of the independent variable on the dependent variable
Types of experimental designs to obtain equivalent groups
- independent group design
- repeated measures design
- match pair design
What is an independent group design?
Randomly assigning participants to experience one of the conditions (between-subject design)
Advantages and disadvantages of independent group design
Advantages:
- Avoid order effects and demand characteristics - Can use treatments with permanent effects - Similarity to "real world" setting
Disadvantages:
- Any detected difference between conditions may be attributed to group differences - Any true differences may not be detected due to low power - Need many participants - Partipant bias and experimenter expectations
How do you create equivalent groups in independent group designs?
- Random assignment
- Use matched pairs (ex. twins, IQ etc…)
- One can never be sure if matching was effective in creating equivalent groups
What is a repeated measures design?
Assigned to participate in all levels of the independent variable (within-subjects design)
- First choice as it reduces measurement error
When is a repeated measures design not possible?
When IV is a subject variable
- ex. transgenic vs. wild type mice, male vs. female
When order effects make it impossible
- ex. effects of 1 treatment is permanent (ex. surgery)
Advantages and disadvantages of a repeated measures design
Advantages:
- Fewer participants, maximize the data collected - Sensitive to detecting differences between IV levels - Less variance in data attributed to error
Disadvantages:
- Order effect - Demand characteristic - Participant bias - Experimental expectations
What are order Effects
The order of presenting treatments effects the dependent variable
- Practice effect - Fatigue effect - Contrast effect
Demand characteristics
- Any feature of a study that might inform the participant of the purpose and consequently affecting their behavior
(may deliberately act to confirm or undermine hypothesis)
Counteract demand characteristics:
- Deception - filler items - placebo - Ask participant what they think the hypothesis is
Participant biases
Placebo effects:
- Use placebo group - Waitlist control condition
Adaptive procedures:
- Staircase design: trials become more and more difficult if the participants gets the questions correct, incorrect = more easy - For cognitive tasks ie. sound levels - Randomize the order to decrease stress on animals (ie. trails don't get more and more difficult each time, the order is randomized)
Where do experimenter expectations come from?
- Treating participants in each condition differently
- Record or interpreting data differently in different conditions
How do you avoid experimenter expectations?
- Use repeated measure design
- Automated presentation of conditions and recording of data
- Double-blind experiment