Experimental Design
The general plan for selecting participants, assigning participants to experimental conditions, controlling extraneous variables, and gathering data. Blueprint for the experiment.
Principle of Parsimony (Occam's razor)
The belief that explanations of phenomena and events should remain simple until the simple explanations are no longer valid.
Independent variable (IV)
A stimulus or aspect of the environment that the experimented directly manipulates to determine its influence on behavior.
Dependent variable (DV)
A response or behavior that the experimenter measures. Changes in the DV should be caused by manipulation of the independent variable.
Extraneous variables
Uncontrolled variables that may unintentionally influence the dependent variable (DV) and thus invalidate an experiments.
Using only 1 IV
Simple. Only using one may be appropriate for an experiment but may not yield all of the answers the experimenter wished to answer. However the combination of multiple single-IV experiments may explain complex phenomena.
How to use only one IV with two groups
The most common manner is to present some amount or type of the IV to one group and withhold it from the second group. The experimenter contrasts the presence with the absence.
Levels (treatment conditions)
Differing amounts or types of an IV used in an experiment
Experimental Group
In a two-group design, the group of participants that received 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 groups so that each participant has an equal chance of being if any group. (putting them in the group) Concerned with control procedures, important as a control strategy. Should equate to any differences betw
Random Selection
A control technique that ensures that each member of the population has an equal chance of being chosen for an experiment. (choosing) Influences the generality of the results.
Independent Groups
Groups of participants formed by random assignment. Degrees of freedom is N-2
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 (Matched assignment)
A method of assigning research participants to groups so that there is 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. To create, measure the participants on a variable that could effect the experiment's DV and then create a groups of equal participants.
Repeated Measure
An experimental procedure in which research participants are tested or measured more than once on each one of the variables. Makes a correlated-group design good.
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 groups through matched pairs, natural pairs, or repeated measures. Comparing scores within the same participants.
Between-Groups Variability
Variability in DV scores that is due to the effects of the IV.
Error Variability
Variability or differneces in DV scores that is due to factors other than the IV, such as individual differences, measurement error, and extraneous variation (also known as within-groups variability).
Goal of Experiment
To maximize he between groups variability and minimize the 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 plan to compare statistically.
Heterogeneity of Variance
Occurs when we do not have homogeneity of variance; 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.