meth test 3

Independent Variable (IV)

Variable manipulated or controlled by the researcher (cause)

Dependent Variable (DV)

Variable measured to see the effect (outcome)

How to identify IV

Ask "What did they change?"

How to identify DV

Ask "What did they measure?"

Control Variables

Variables kept constant to prevent affecting results

Levels of IV

Specific variations of the independent variable

Manipulated Variable

Variable the researcher directly controls

Between-subjects design

Another name for independent-groups design

Independent-groups design

Different participants in each condition

Within-groups design

Same participants in all conditions

Matched-groups design

Participants matched on traits before assignment

Posttest-only design

Measures DV only after manipulation

Pretest/Posttest design

Measures DV before and after manipulation

Repeated-measures design

Participants measured after each condition

Concurrent-measures design

Participants exposed to all conditions at once

Double-blind study

Neither participants nor researchers know group assignments

Random Assignment Purpose

Makes groups similar at the start

Internal Validity

Ensures only IV caused change in DV

Random Selection

Choosing participants from population for generalization

Selection Effects

Groups differ at the start

Carryover Effects

Previous condition affects later condition

Practice Effects

Improvement from repeating a task

Demand Characteristics

Participants guess purpose and change behavior

Counterbalancing

Changing order of conditions to avoid order effects

Design Confound

Second variable that varies with IV

Order Effects

Results affected by order of conditions

Why use within-groups

Fewer participants and same people in all conditions

Within-groups threat

Order effects

Types of order effects

Practice, fatigue, carryover, testing

Missing element in one-group pretest/posttest

A comparison group

Attrition

Participants dropping out

Fix for attrition

Remove extreme pretest scores

Null Results Reasons

Weak manipulation or too much variability

Ceiling Effect

Scores cluster at high end (too easy)

Floor Effect

Scores cluster at low end (too hard)

Unsystematic Variability

Error variance or noise

Reduce Measurement Error

Use reliable tools and larger sample

Double-blind alternative

Masked design or blind observer

Placebo Study Purpose

Separate real effect from expectations

Situation Noise

External distractions affecting results

Increase Precision

Stronger manipulation, control, larger sample

Pretest/Posttest vs One-group

Includes comparison group vs none

Factorial Design

Uses 2 or more independent variables

Factor

Another name for IV in factorial design

Interaction Effect

Effect of one IV depends on another

Main Effect

Overall effect of one IV

Number of Main Effects

One for each IV

Interactions vs Main Effects

Interactions can exist without main effects

Number of Conditions

Multiply levels of IVs

Marginal Means

Averages across levels of other IV

Noise (factorial)

Variability within groups

External Validity

Generalization to real world

Purpose of External Validity

Ensure results apply beyond lab

Advantage of Factorial Designs

Can test interactions and multiple variables