PSY 311 Experimental Designs Chapter 8

James Madden

What is the key feature of an experiment?

The researcher manipulates the independent variable (IV) and measures the dependent variable (DV).

Why are experiments stronger than non-experimental designs?

They can rule out alternative explanations like directionality problems and confounding variables.

What is the directionality problem?

When it’s unclear whether A causes B or B causes A.

What are confounding variables?

External factors that may influence both the IV and DV.

What is random assignment?

Assigning participants to conditions randomly so groups are similar before manipulation.

Why is random assignment important?

It prevents selection bias and helps ensure differences are due to the IV.

What is a posttest-only design?

Participants are randomly assigned, the IV is manipulated, and the DV is measured only after.

What is an advantage of a posttest-only design?

Strong internal validity due to random assignment.

What are disadvantages of a posttest-only design?

Cannot confirm groups were equal before, cannot measure change, cannot tell which condition caused change.

What is a pretest-posttest design?

Measure DV, randomly assign participants, manipulate IV, then measure DV again.

What are advantages of a pretest-posttest design?

Can assess group equivalence and measure the amount of change.

What are disadvantages of a pretest-posttest design?

Time-consuming and pretest may create demand characteristics.

What is a between-subjects design?

Each participant is in only one condition.

What is an advantage of a between-subjects design?

Avoids testing, fatigue, and sequence effects.

What is a disadvantage of a between-subjects design?

Groups may differ despite random assignment.

What is a within-subjects design?

Participants experience all conditions.

What is an advantage of a within-subjects design?

Eliminates preexisting differences between groups.

What are disadvantages of a within-subjects design?

Testing effects, fatigue effects, and sequence effects.

What are testing effects?

Performance improves due to practice rather than the IV.

What are fatigue effects?

Performance worsens due to tiredness or boredom.

What are sequence effects?

Performance in one condition is influenced by a previous condition.

What is counterbalancing?

Varying the order of conditions to control for sequence, fatigue, and testing effects.

What are the two main groups in a basic experiment?

Experimental group (receives manipulation) and control group (does not).