In an experiment, variables are measurable elements that can vary or take on different values along dimension.
Validity means the operational definition accurately manipulates the independent variable or measures the dependent variable.
An experiment is confounded when the value of an extraneous variable systematically changes along with the independent variable.
Main Features of Psychological Experiment
We manipulatetheantecedentconditionstocreateatleasttwodifferenttreatmentconditions.
We exposesubjectstodifferenttreatmentconditionssothatwecanmeasuretheeffectsofthoseconditionsonbehavior.
We record the responses or behaviors of subjects undervariousconditions and them comparethemusingstatistics.
We then assesswhetherour predictions areconfirmed.
An operationaldefinition specifies the exact meaning of a variable in an experiment by defining it in terms of observable operations, procedures, and measurements.
An independentvariable (IV) is the variable (antecedent condition) an experimenter intentionally manipulates.
Reliability refers to the consistency of experimental operational definitions and measured operational definitions.
A dependentvariable is the outcome measure the experimenter uses to assess the change in behavior produced by the independent variable.
Each IV and DV has 2 definitions: (1) conceptualdefinition (used in everydaylanguage); (2) operationaldefinition (used in carryingouttheexperiment).
The experimentalhypothesis expresses a potential relationship between 2 kinds of variables – the IV and the DV.
There are 2 kinds of operational definitions: experimental and measured.
Levels of an independent variable are the values of the IV created by the experimenter.
Interrater reliability is the degree to which observers agree in their measurement of the behavior.
Confounding variable is an outside influence that changes the effect of IV and DV.
Constructvalidity is how accurately an operational definition represents a construct.
An experimentaloperationaldefinition specifies the exact procedure for creating values of the independent variable.
Subjectmortalitythreat occurs when subjects drop out of experimental conditions at different rates.
Facevalidity is the degree to which the validity of a manipulation or measurement technique is self-evident.
The dependentvariable depends on the value of the independent variable.
Main Features of Psychological Experiment
When conducted skillfully, an experiment allowsustomakecauseand-effectstatementsaboutbehavior.
If behavior changes as the antecedent conditions change, we can say that the differencesinantecedentconditionscausedthechangesinbehavior
Historythreat occurs when an event outside the experiment threatens internal validity by changing the dependent variable.
Test-retestreliability means the degree to which a person's scores are consistent across two or more administrations of a measurement procedure.
The need for operational definitions becomes easily apparent when we zero in on variables that are actually hypotheticalconstructs or concepts.
Internalvalidity is the degree to which changes in the dependent variable across treatment conditions were due to the independent variable.
A measuredoperationaldefinition specifies the exact procedure for measuring the dependent variable.
Statisticalregressionthreat occurs when subjects are assigned to conditions on the basis of extreme scores, the measurement procedure is not completely reliable, and subjects are retested using the same procedure to measure change on the dependent variable
An experiment requires at least two levels.
IndependentVariable
4 types of validity:
Face validity
Content validity
Construct validity
Internal validity
Randomization (aim is random distribution of confounders between study groups)
Internalvalidity establishes a cause-and-effect relationship between the independent and dependent variables.
Constructs cannot be observed directly, but we can infer their existence from behaviors that we can observe.
OperationalDefinition
Maturationthreat is produced when physical or psychological changes in the subject threaten internal validity by changing the DV.
Restriction (restrict entry to study of individuals with confounding factors – risks bias in itself)
Content validity means how accurately a measurement procedure samples the content of the dependent variable.
2 types of Operational Definition:
Experimental operational definition
Measured operational definition
Matching (of individuals or groups, aim for equal distribution of confounders)
Confounding occurs when an extraneous variable systematically changes across the experimental conditions.
2 types of Reliability:
Interrater reliability
Test-retest reliability
Stratification (confounders are distributed evenly within each stratum)
Because we manipulate the IV and measure its effects on the DV, the latter are sometimes called dependent measures.