Learn: Exam 3 - Exp Methodology

Independent Variable (IV)

The variable manipulated or changed by the researcher; the presumed cause in an experiment.

Dependent Variable (DV)

The variable measured by the researcher; the outcome being studied.

Control Variables

Variables kept constant throughout an experiment so they do not influence the results.

Manipulated Variable

A variable deliberately changed or controlled by the researcher; usually the independent variable.

Levels of an Independent Variable

The different values or conditions of an independent variable.

Conditions

The specific experimental situations participants experience, determined by the levels of the independent variables.

Independent-Groups Design (Between-Subjects Design)

Different participants are assigned to different conditions; each participant experiences only one level of the independent variable.

Within-Groups Design (Within-Subjects Design)

Every participant experiences all levels of the independent variable; participants serve as their own comparison.

Matched-Groups Design

Participants are paired based on similar characteristics and assigned to different experimental conditions.

Pretest/Posttest Design

Participants are measured before and after an intervention to determine whether changes occurred.

One-Group Pretest/Posttest Design

One group is measured before and after an intervention; does not have a control group.

Posttest-Only Design

Participants are measured only after the experimental treatment; no pretest is given.

Repeated-Measures Design

Participants are measured multiple times across different conditions or time points; a type of within-groups design.

Concurrent-Measures Design

Participants experience multiple conditions and provide responses that allow researchers to compare the conditions.

Double-Blind Study

Neither participants nor researchers interacting with them know who receives which treatment; reduces expectancy effects and bias.

Single-Blind Study

One party, usually the participants, does not know which treatment they are receiving.

Double-Blind Placebo-Controlled Study

One group receives the actual treatment and another receives a placebo; neither participants nor researchers know who receives which treatment.

Placebo

A fake treatment that looks like the real treatment but contains no active ingredient.

Random Assignment

Participants are randomly placed into different experimental conditions; helps create equivalent groups and prevents selection effects.

Random Selection

Participants are randomly chosen from a larger population; helps create a representative sample and improves generalizability.

Selection Effects

Occur when groups differ systematically before an experiment begins; threaten internal validity.

Main Priority of Experimental Studies

Establishing a cause-and-effect relationship through manipulation, control, and random assignment.

Order Effects

Occur when the order in which participants experience conditions influences their performance.

Practice Effects

Participants improve because they have completed a task before.

Fatigue Effects

Participants perform worse because they become tired or bored.

Carryover Effects

Effects of one experimental condition influence performance in a later condition.

Counterbalancing

Researchers vary the order in which participants experience conditions to control order effects.

Demand Characteristics

Cues that reveal the purpose or expectations of a study to participants, potentially causing them to change their behavior.

Observer Bias

Occurs when a researcher's expectations influence how they observe, measure, or record participants' behavior.

Design Confound

An additional variable that systematically changes along with the independent variable, making it difficult to determine the cause of results.

Measurement Error

The difference between the actual value and the measured value; can result from inaccurate tools or incorrect readings.

Measurement Reliability

The consistency of a measurement across repeated uses or occasions.

Unsystematic Variability

Random differences or fluctuations in research data; also known as error variance.

Error Variance

Variability in results that is not explained by the independent variable; also called unsystematic variability.

Situation Noise

External distractions or environmental factors that interfere with an experiment, create variability within groups, and reduce precision.

Attrition

Occurs when participants drop out of a study before it is completed.

Attrition Analysis

Comparing participants who dropped out with those who stayed to determine whether they differed in important ways.

Null Result

A result in which a study does not find a statistically significant effect or relationship; does not necessarily mean there is no effect.

Ceiling Effect

Occurs when a measurement is too easy or scores are near the maximum, making improvement difficult to detect.

Floor Effect

Occurs when a measurement is too difficult or scores are near the minimum, making differences difficult to detect.

Precision

How accurately a study estimates the true effect or population value; greater precision means less uncertainty.

Statistical Power

The probability that a study will detect a real effect when one exists.

Sample Size

The number of participants in a study; larger samples generally produce more precise estimates and increase statistical power.

Confidence Interval (CI)

A range of values estimating where the true population value may fall.

Narrow Confidence Interval

Indicates greater precision and less uncertainty.

Wide Confidence Interval

Indicates less precision and more uncertainty.

Factorial Design

An experimental design involving two or more independent variables; allows researchers to examine main effects and interactions.

Factors

Another name for independent variables in a factorial design.

Levels

The different conditions or values within each independent variable.

Main Effect

The overall effect of one independent variable on the dependent variable, averaged across the levels of the other independent variables.

Overall Effect

Another name for a main effect.

Simple Difference

The difference between two means at a particular level of another independent variable; helps explain an interaction.

Interaction Effect

Occurs when the effect of one independent variable depends on the level of another independent variable.

Marginal Means

The means calculated for each level of one independent variable, averaging across the levels of the other independent variable.

Internal Validity

The extent to which a study establishes that the independent variable caused changes in the dependent variable.

External Validity

The extent to which research findings can be generalized to other people, settings, situations, and times.

Generalizability

The extent to which research findings apply to populations or situations beyond the original study.