ABA glossary
Variable ratio
Also called VR
Definition
A schedule in which reinforcement follows a number of responses that varies unpredictably around an average. On VR 4, reinforcement might come after 2, then 6, then 4 responses.
In plain words
Because the learner cannot predict which response will pay off, every response has a chance of producing reinforcement. That produces high, steady rates with little pausing, and behavior on a VR schedule keeps going for a long time after reinforcement stops (it is resistant to extinction). Slot machines and sales calls are the usual everyday examples.
Example from a session
Once Mila reliably answers social questions, her BCBA changes the program from CRF to VR 3. The data sheet lists a mixed sequence (2, 4, 3, 1, 5, 3) so the RBT knows when to deliver praise and a sticker. Mila keeps answering at a steady pace and does not slow down after a sticker. The RBT follows the written sequence instead of reinforcing "sometimes," because guessing tends to drift into a thinner or less consistent schedule than the plan calls for.
For BCBA candidates and supervisors
VR schedules are useful for maintenance because they resemble natural reinforcement and resist extinction. The same property makes intermittently reinforced problem behavior hard to extinguish: a caregiver who gives in only now and then has, in effect, put the behavior on a variable schedule, so extinction plans have to be followed every time. When moving from CRF to VR, analysts thin gradually and watch for ratio strain.
Often confused with variable interval, fixed ratio
Both variable schedules make reinforcement unpredictable, but VR depends on the number of responses and VI depends on time. On VR, responding faster earns reinforcement sooner; on VI it does not, which is why VI produces moderate rather than high rates. Compared with FR, VR removes the predictable pause after each reinforcer.
Exam tip
Think "unpredictable count." VR produces the highest, steadiest rates of the simple schedules and strong resistance to extinction. Stems about gambling, sales calls, or a parent who gives in only sometimes are classic VR cues.
Can you spot variable ratio in a scenario?
Practice BCBA B.9 with exam-style questions and instant feedback.