Parsimony simply means that when conducting a scientific experiment to always choose the most simple explanation. The classic example, “If you hear hoofbeats, think horse — not zebra.”

Here are some examples of parsimony in ABA terms. 

  • Every day after school, Joe gets off the bus, walks into the kitchen and cries. His mom gives him a cookie as soon as he starts crying in order to calm him down and Joe stops crying as soon as he gets the cookie every time. Joe is non verbal and cannot tell his mom why he is crying. Joe’s mom thinks that Joe is sad to get off the bus because he likes riding on the bus. In this example, using the law of parsimony, the correct response would be to determine if Joe’s crying is maintained by receiving a cookie which is a much more simple explanation. 
  • Peter claps his hands randomly during class. A board certified behavior analyst (BCBA) was called in to write a behavior plan to address this. His teacher said he thinks that Peter is waiting for the precise moment that he is about to get to an important point in his lesson and that clap his hands in order to make the teacher mad. When a functional analysis was conducted, it was determined that there is no clear antecedent for the behavior and it occurs across all conditions at the same rate. The more simple explanation for this is that the behavior is automatically maintained.
  • During an ABA session, a child keeps scratching his diaper. The behavior technician calls the BCBA and states her concern that a new behavior is developing that needs to be addressed right away. Before the BCBA observes the behavior, she calls mom to ask if the child could be itchy from a diaper rash. 

This article is useful for registered behavior technicians (RBT) or students who are studying to become board certified behavior analysts (BCBAs). Understanding (Applied Behavior Analysis) ABA terms is critical for both being an effective ABA therapist and passing your BCBA exam.

In an effort to help you study for your BCBA exam more effectively, this post is written in a “study note” form rather than as a long form blog post. They are my personal study notes I am sharing with you as a gift. I am spending my time studying so they are not edited. I am grateful for your understanding in overlooking the grammar!  Happy Studying! 


Cooper, J. O., Heron, T. E., & Heward, W. L. (2007). Applied Behavior Analysis (3rd Edition). Hoboken, NJ: Pearson Education.

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