ABA glossary
Multielement design
Also called alternating treatments design
Definition
A single-case design that rapidly alternates two or more conditions, each linked to a distinct stimulus, and compares their effects by how far apart their data paths are. Also called an alternating treatments design.
In plain words
Instead of running long phases, a multielement design switches between conditions quickly, often every session or even within a day, in a counterbalanced order. Each condition gets its own data path on the graph. If the paths separate clearly and consistently, the conditions are having different effects. It can compare treatments without a long baseline and without withdrawing treatment, and it is the design used in most functional analyses.
Example from a session
A BCBA compares two ways of teaching sight words to Ava: flashcards and a reading game. Sessions alternate in a random order, with blue folders for flashcards and green folders for the game, as the protocol says, and each method teaches its own set of equally difficult words. The RBT uses the right folder for each session and records words read correctly. By the third week, the game's data path sits well above the flashcards' path, so the game is more effective for Ava.
For BCBA candidates and supervisors
Multielement designs require that the conditions be discriminable (hence distinct stimuli) and that behavior can change quickly. Their main threat is multiple-treatment interference, where one condition's effects carry over to another, so analysts counterbalance order and may follow up with the winning condition alone. Results show which condition works better within the comparison, not how it would work on its own over time. Functional analyses typically use this design, with test conditions compared against a control.
Often confused with reversal design, multiple-treatment interference
A multielement design alternates conditions rapidly and compares data paths; a reversal design moves through longer phases and compares behavior before and after each change. Multiple-treatment interference is not a design but the main risk of this one: exposure to one condition affecting behavior in another.
Exam tip
"Rapidly alternating" or "alternating by session," with separate data paths for each condition, means a multielement (alternating treatments) design. If the question asks for its main threat, choose multiple-treatment interference.
Can you spot multielement design in a scenario?
Practice BCBA D.7 with exam-style questions and instant feedback.