How often have we sat in meetings with other professionals such as OTs, PTs, reading specialists, and diagnosticians, nodding our heads along with their descriptions of the goals that our shared clients and students are working on. Yes, we “share” children. To think that this is the norm indicates that we may have fallen prey to a form of bias called conjunction fallacy. Worse yet, without knowing about it, we could misdiagnose or negatively impact the referral process.

The conjunction fallacy is jumping to the conclusion that two events together (conjunction), are more likely than one or both of the events separately. The truth is always that the probability of two events occurring together (in “conjunction”) is less than or equal to the probability of either one occurring alone.

The conjunction fallacy is my favorite form of bias because no matter how well I wrap my brain around it, I will guess wrong every time I see two diagnoses together. Here’s what it looks like for me:

Another professional leans her head in my door and says:

“Hey, Steven is on my caseload and I am working on X. Do you think you should take a look at him?”

“Sure,” I say (every time).

I don’t know Steven, or anything about Steven. And yet, because he has a completely different diagnosis or set of goals, I am ready to completely skip the referral process and “take a look,” which can be misconstrued as a rubber stamp that Steven has a problem.  

Where there’s smoke, there’s fire is actually incorrect.
Where there is smoke, there is smoke.

Let’s use our time here to participate in a short but cool experiment to feel the conjunction fallacy taking shape in our own brains (the betrayal!) and then talk about how it crops up in special education. We will end with a couple tips on how to be on the lookout for it.

Understanding the Conjunction Fallacy: Insights from Logic and Psychology

At its core, the conjunction fallacy defies basic logic. To make the point, let’s start with three questions for you to play along:

How many words can you think of that have N as the second to last letter?

How many words can you think of that end in ING?

Are there more ING words or words that have N as the second to last letter?

Got your answer? Now watch this video:

Pretty neat way to understand the conjunction fallacy, isn’t it?

Cognitive bias extends beyond word games and is more telling in the medical experiment they discussed. Even seasoned medical professionals, when presented with a list of symptoms and conditions, are prone to overestimate the likelihood of concurrent ailments. The allure of complexity often clouds our judgment, leading us to believe that the combination of symptoms carries greater weight than individual conditions alone.

Conjunction Fallacy in Speech Language Pathology

In terms of being an SLP, one place I see this as being really problematic is how we also associate disorders when making a diagnosis. Here’s another question:

What is more likely a child with a language disorder or a child with a language disorder and a learning disability?

Hopefully you are savvy enough now to see that the chance of a single disorder is always more probable. But even as I am writing these words, my mind is being populated with all my favorite students that I shared with the OTs and PTs. I am also thinking about all the kids I pick up from the Special Education classroom.

Share this Information with Colleagues in the Schools

There is a general disdain for the referral process in many school districts because it is seen as being cumbersome and creating more problems than solutions. No argument here. However, is there a chance that we are contributing to the confusion?

My experience is that my teachers and other special educators are extremely smart with loads of experience and opinions that I respect. When they qualify a new student and see other issues, it is my role as the communication specialist to weigh in and help out. This makes me a team member, and I genuinely enjoy the collaboration.

Because the student has already been in the evaluation process for a while, there is a nervous desire to “fast track” the student so that they are not in the referral process for another 60 days. Totally valid, move them up in your queue to make good on the promise to the principal and parents to have the child evaluated in a timely manner. However, treat each child like a new referral for communication, not the continuation of one.

How to Reduce SLP Susceptibility to the Conjunction Fallacy: Key Takeaways

  • Bet on typicality – You may be surprised!
  • Take referrals from your diagnostician seriously, but don’t assume that just because they qualified for something else, that they will also qualify for speech services. 
  • There are definite “correlations” between impairments; phonology and reading difficulties, reading difficulties and language difficulties, but you need your own data.
  • In referral packets, look for specific concerns that talk about communication problems, not just math, reading, writing, or behavior. In a case study we presented in the course Collaborating with Educational Diagnosticians and LSSPs in the Referral-Evaluation Process, we found that in every referral that an educational diagnostician sent on to us without communication being cited by parent and/or teacher, the child did not qualify.
  • Thank colleagues for putting kids on our radar if there are concerns, but get all the referral data, even if it is fast-tracked.
  • Accept referrals from doctors who have complex cases, but don’t be afraid to say that communication is a relative strength, rather than another diagnosis.

The conjunction fallacy serves as a poignant reminder of the intricate interplay between probability and perception. In the field of speech pathology, it poses unique challenges, particularly in the assessment and diagnosis of language disorders. Let’s all continue to approach each case with discernment, gathering independent data to form an accurate diagnosis.

7 Types of Bias and How They Affect Speech Language Pathology

This is one of eight essays we wrote on bias, based on the work of Daniel Kahneman and the research we put together for the ASHA CEU course: How Ethics and Biases Shape Our Decisions: A Fun Look at Research on Heuristics. Start with the inspirational article on Daniel Kahneman and then work your way through seven ways our hidden biases can unknowingly influence our thinking.

Overview: Celebrating Daniel Kahneman (3/5/1934 – 3/27/2024) and His Enormous Impact on Bias and Our Work

  1. Navigating Fairness Bias in Our Role as SLPs
  2. Framing Effect: Shaping Perspectives with Words
  3. Understanding Availability Bias: Challenging Perceptions During Evaluations
  4. Deciphering the Conjunction Fallacy – Overlap or Isolation of Disorders?
  5. The Overconfidence Effect – Misperceptions About Amount of SLP Work and How Long it Takes
  6. Embracing Loss Aversion: Balancing Risk and Reward in Speech Pathology
  7. Freedom from the Anchoring Effect: When Numbers Work Against Us

How Ethics and Biases Shape Our Decisions: A Fun Look at Research on Heuristics

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