ABA glossary
Operational definition
Definition
A description of a target behavior in observable, measurable terms, including what counts, what does not, and when an episode starts and ends, so that different observers identify and record each instance the same way.
In plain words
An operational definition turns a vague label into something two people can count the same way. "Aggressive" or "upset" means different things to different people; "strikes another person with an open or closed hand, with enough force to make a sound" does not. A good definition names the behavior's observable features, gives examples and non-examples, and states onset and offset rules (for example, "an episode ends after 30 seconds with no crying"). It should describe what the person does, not why they do it or how they feel.
Example from a session
An RBT's data sheet says to record "elopement." The written definition reads: "Leaving the assigned area by more than 3 feet without adult permission; walking to the bathroom with a pass does not count." When Ty walks to the door to get his jacket after the teacher said "Go get your jacket," the RBT does not score it. Because the definition is written down, a second observer would make the same call.
For BCBA candidates and supervisors
Analysts choose between function-based definitions (every response that produces the same effect, such as any way of leaving the group) and topography-based definitions (the form itself, such as a correct sign). Function-based definitions are usually preferred because the effect is what matters, while topography-based ones fit when the form is the skill. Definitions are tested before baseline: if two trained observers disagree, the team clarifies the definition and checks observer training before collecting baseline. A shift in how observers apply the definition (observer drift) or changes mid-intervention makes the data across phases incomparable, which threatens every later decision.
Often confused with behavioral objective, label vs. behavior
An operational definition says what the behavior is so it can be measured; a behavioral objective says what the learner should achieve, under what conditions, and to what criterion. A label such as "defiant" summarizes or interprets behavior; an operational definition replaces the label with what was actually seen or heard.
Exam tip
Pick the option two strangers could score the same way without asking the writer what was meant. Reject options with feelings, intent, or labels ("frustrated," "wants attention," "being rude"), and favor ones with clear start and stop rules and non-examples.
Can you spot operational definition in a scenario?
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