Advanced Research Methods Chapter 9: Experimental Designs: Within-Subject

Threats to internal validity in within-subjects

Environmental variables, Time-related variables, Order effects, Carry-over effects.

Time related threats

History (outside event), Maturation, Instrumentation, Regression towards the mean.

Counterbalancing

Changing the order in which conditions are applied from one participant to another. Doesn't actually eliminate order effects, but spreads them out.

Within-subjects Advantages

Few participants, Eliminates individual difference problems, Reduces variance.

Within-subjects Disadvantages

Potential time-related factors, Participants attrition.

3 main factors that differentiate the designs

Individual differences, Time-related factors and order effects, Number of participants.

Matched-subjects designs

Uses a separate group for each condition. Each individual in one group is matched to another. (ex. brain injury).