Experimental Design
The general plan for selecting participants, assigning participants to experimental conditions, controlling extraneous variables and gathering data
Principle of Parsimony
The belief that explanations of phenomena and events should remain simple until the simple explanations no longer valid
Independent Variable
A stimulus or aspect of the environment that the experimenter directly manipulates to determine its influences on behavior
Dependent Variable
A response or behavior that the experimenter measures. Changes in the DV should be caused by manipulation of the IV
Extraneous Variables
Uncontrollable variables that may unintentionally influence the dependent variable and thus invalidate the experiment
Levels
differing amounts or types of an IV used in an experiment (also known as treatment conditions)
Experimental Group
In a two-group design, the group of participants that receives the IV
Control Group
In a two-group design, the group of participants that does not receive the IV
Random assignment
A method of assigning research participants to group so that each participant has an equal chance of being in any group
Random Selection
A control technique that ensures that each member of the population has an equal chance of being chosen for an experiment
Independent Groups
Group of participants formed by random assignment
Between-Subjects comparison
Refers to a contrast between groups of participants who were randomly assigned to groups
Confounded Experiment
An experiment in which an extraneous variable varies systematically with the IV, which makes drawing a cause-and-effect relation impossible
Correlated Assignment
A method of assigning research participants to groups so that there is a relationship between small numbers of participants; these small groups are then randomly assigned to treatment conditions (also known as paired or matched assignment)
Matched Pairs
Research Participants in a two-group design who are measured and equated on some variable before the experiment
Repeated Measure
An experimental procedure in which research participants are tested or measured more than onece
Natural Pairs
Research Participants in a two group design who are naturally related in some way (e.g. a biological or social relationship)
Within-subjects comparison
Refers to a contrast between groups of participants who were assigned to group through matched pairs, natural pairs, or repeated measures
Between Groups Variability
Variability in DV scores that is due to the effects of the IV
Error Variability
Variability in DV scores that is due to factors other than the IV, such as individuals differences, measurement error, and extraneous variation (also known as within-groups variability)
Degrees of Freedom
The ability of a number in a specified set to assume any value
True experiment
An experiment in which the experimenter directly manipulates the IV
Ex Post Facto Research
A research approach in which the experimenter cannot directly manipulate the IV but can only classify, categorize or measure the IV because it is predetermined in the participants (e.g. IV=sex)
Homogeneity of Variance
The assumption that the variances are equal for the two (or more) groups you plant to compare statistically
Heterogeneity of Variance
Occurs when we do not have homogeneity of variance; this means that our two (or more) groups' variances are not equivalent
Robust
Refers to a statistical test that can tolerate violation of its assumptions (e.g. homogeneity of variances) and still yield valid results
Positive Correlation
As scores on one variable increase, scores on the second variable also increase
Negative Correlation
As scores on one variable increase, scores on the second variable decrease