Experimental Psychology Ch. 10

Define IV and DV.

manipulated and measured variables

What are the three characteristics present in experiments that support causal statements?

1. Covariance. Is the causal variable related to the effect variable? Are distinct levels of the independent variable associated with different levels of the dependent variable?
2. Temporal precedence. Does the causal variable come before the effect varia

Identify and define the two potential threats to internal validity.

� Design confounds
� Second variable that varies systematically with the IV
� Selection effects
� Participants in one group are systematically different from participants in other group(s)

How could you control for selection effects?

� Random assignment
� Matched-groups design

In general, what is an independent-groups design?

Independent-groups design involves different groups of participants being placed into different levels of the independent variable. Also called a between-subjects design or a between-groups design.

Give an example of an independent-groups posttest-only design.

In the posttest-only design, also known as an equivalent groups, posttest-only design, participants are randomly assigned to independent variable groups and are tested in the dependent variable once.

Give an example of an independent-groups pretest/posttest design.

In a pretest/posttest design, or equivalent groups, pretest/posttest design, participants are randomly assigned to at least 2 groups and are tested on the key dependent variable twice - once before and once after exposure to the independent variable.

Discuss the costs and benefits of a pretest/posttest design.

� Evaluate effectiveness of random assignment
� Evaluate how participants change over time
� Can make the research question obvious to the participants
� Can decrease the validity of the measure

In general, what is a within-groups design?

In a within-groups design, or within-subjects design, there is only one group of participants, and each person is presented with all levels of the independent variable.

Give an example of a concurrent-measures design.

In a concurrent-measures design, participants are exposed to all the levels of an independent variable at roughly the same times, and a single attitudinal or behavioral preference is the dependent variable.

Give an example of a repeated-measures design.

A repeated-measures design is a type of within-groups design in which participants are measured on a dependent variable more than once �- that is after exposure to each level of the independent variable.

Discuss the costs and benefits of a within-groups design.

� Advantages:
� Ensures equivalency across groups
� Increased statistical power
� Disadvantages:
� Order effects
� Demand characteristics
� Inappropriate if IV causes permanent change in DV

Identify and describe the three order effects.

� Practice effect
� Fatigue effect
� Contrast effect

What are the two potential solutions for order effects?

� Partial counterbalancing
� Complete counterbalancing