Experimental Design Flashcards
what is the experimental approach?
The researcher manipulates one or more variables and controls and measures any change in other variables.
what are the variables in experimental research?
independent variabel (IV)
dependent variable (DV)
extraneous variable (EV)
what is the independent variable?
The variable that is manipulated
what is the dependent variable?
The variable that is measured
what is the extraneous variable?
A variable that might have an influence on the DV but is not in the focus of interest
what is a confound?
A confound is any uncontrolled extraneous variable that co-varies with the independent variable and could provide an alternative explanation of the results
what are the types of independent variables?
situational variables
task variables
instructional variables
what are situational variables?
Features in the environment that participants may encounter (e.g. number of bystanders in an experiment on helping)
what are task variables?
Vary the type of tasks performed by participants (e.g. different problems in a problem solving experiment)
what are instructional variables?
Vary the type of instruction participants get (e.g. perform a memory task by trying to form a mental image of the item or not)
what are subject variables?
Independent variables that are not directly manipulated by the experimenter such as natural groups (e.g. age groups, gender) or participant variables (e.g. political attitude, religious beliefs).
what are the problems with subject variables?
- cannot be independently manipulated
- therefore causal inferences are problematic
- differences in the DV between groups can be caused by any other factor on which the groups differ.
which groups are control group experiments made of?
- Experimental group: Gets a specific treatment or manipulation.
- Control group: Does not get an effective treatment or manipulation.
what are problems with the dependent variable?
- ceiling effects
- floor effects
what are ceiling effects?
The average scores for the DV are so high that no difference can be determined between conditions.
what are floor effects?
The average scores for the DV are so low that no difference can be determined between conditions.
what is the regression to the mean?
There is a statistical tendency for people who score extremely low or high on a test to score closer to the middle the next time.
what can be done to control extraneous variables? (5)
- Keeping the variable constant across experimental groups (e.g. only include people with specific face recognition abilities)
- Build the EV into design to investigate it (e.g. including face recognition abilities as a factor in the design)
- Matching the groups regarding the EV
- Random assignment to experimental groups
- Statistically controlling the variable (e.g. measuring the extraneous variable and statistically considering the influence)
what are the forms of validity in experimental research?
- external validity
- internal validity
what is the external validity?
The extent to which one can generalize the findings of a study to other situations, people, settings and measures.
what are the main criticisms of external validity?
- participants
→ Most studies in cognitive and social psychology are carried out with participants from WEIRD (Western, Educated, Industrialized, Rich, and Democratic) societies. - Experimental setting
→ Experimental settings are artificial and completely detached from real life. They lack ecological validity.
what is internal validity?
Internal validity is the degree of confidence that the causal relationship you are testing is not influenced by other factors or variables
threats to internal validity (studies extending over time)
- History: An unrelated event influences the outcomes
- Maturation: The outcomes of the study vary as a natural result of time.
- Instrumentation: Different measures are used in pre-test and post-test phases
- Testing: The pre-test influences the outcome of the post-test.
threats to internal validity (participant problems)
- Selection bias: Groups are not comparable at the beginning of the study
- Attrition: Dropouts from participants