Repeated Measures Designs

Psyc 210

Repeated Measures Designs

Each person participates in both the experimental and control condition. Basically the same group of people are being tested repeatedly.

Advantages of RMD’s

Fewer participants, more efficient, more sensitive because of reduced error variability, and allows you to assess changes over time.

Sensitive test

More likely to see what errors you can avoid. Less prone to type 2 error.

Internal validity

The degree to which the researcher can say variables within the study are truly related.

Threats to Internal Validity

Possible alternative explanations for a study’s findings. Other things taht could affect your results that are not the IV.

Practice effects

Changes participants undergo as a result of repeated testing in RMDs. Ex: I got better at ___ because I did it multiple times throughout the day. MOST IMPORTANT FOR RMDs. Major threat to internal validity of RMDs.

Counterbalancing (how we avoid practice effects)

A technique for spreading potential practice effects out evenly across condition.

Differential Transfer

Performance in one condition differs depending on the condition that precedes it. May occur when the subject can’t stop doing A even though they’re supposed to do B. This condition is at the nuclear level of practice effects. IGD must be used instead.

Instrumentation

Occurs when a method of assessing one of the variables in a study changes during data collection. Something breaks, something new must be used.

Maturation

Occurs when a change in the dependent variable could be attributed to passage of time.

History

When something outside of the experiment beyond control of the researchers may have influenced the experiment’s outcome. Ex: flood, forrest fire, etc.

Experimenter Bia

When researcher differentially interprets data based on their knowledge of whether participants are receiving the experimental or control condition.

Double Blind Study

No knowledge of people in groups (what condition they pertain to) Participants have no knowledge of their condition.

Participant Reactiivty

When participants alter their behavior because they know they’re being observed by the researchers.

Testing

When participants are given the same test twice, and as a result, perform better or particularly consistently upon second testing. To avoid, don’t do a pretest.