Lecture 15 – Single Subject Designs Pt 2.
• ABA – second baseline added following “withdrawal” of treatment
o What is benefit of ABA? (didn’t mention in last lecture)
Gives us increase in confidence that ∆A is causal to ∆B
• ABAB – second baseline, “withdrawal”, and second treatment
Back to ABAB designs:
Two Major Problems:
• The DV must be reversible, and many outcomes of interest are not fully
reversible (at least not within a short interval)
o Ie. Fitness training for the B phase may change cardiovascular parameters
in a way that bleeds over into the second A (baseline) phase
• Even if theoretically reversible, it may be unethical to withdraw the treatment
o Ie. experimental cancer drug that halts apoptosis within an individual
Beyond the AB design
• Threats of internal validity to AB designs
• Additional control needed via replication of effects!
• Replication across multiple:
o application of trials occur at different times
o we can see a lag in time of application between subjects
o why lag?
Enhances internal validity because it identifies specifically the