In Why I Do Not Attend Case Conferences[7] (1973), psychologist Paul Meehl discusses several fallacies that can arise in case conferences that are primarily held to diagnose patients. These fallacies can also be considered more general errors of thinking that all individuals (not just psychologists) are prone to making.
Barnum effect: Making a statement that is trivial, and true of everyone, or (in case conferences) of all patients, and is thus useless for discussion. Everyone will agree on it, but it will not provide any incremental help in diagnosis.
sick-sick fallacy ("pathological set"): The tendency to have our own stereotypes of what is "healthy", based on our own experiences and ways of being, and identifying others who are different from ourselves as "sick". Meehl emphasizes that though psychologists claim to know about this tendency, most are not very good at correcting it in their own thinking.
"me too" fallacy: The opposite of sick-sick, thinking that "anybody would do this". Minimizing a symptom without considering the objective probability that a mentally healthy person would experience it. Is this really a "normal" characteristic?
Uncle George's pancake fallacy: A variation of "me too", this refers to minimizing a symptom by calling to mind a friend/relative who exhibited a similar symptom, thereby implying that it is normal and common. Meehl points out that the proper conclusion in this comparison is not that the patient is healthy by comparison, but that your friend/relative is unhealthy by comparison.
Multiple Napoleon's fallacy: "It's not real to us, but it's 'real' to him." A theoretical turn that Meehl sees as a waste of time. There is a distinction between reality and delusion, and it is important to make this distinction when assessing the patient. Pondering the patient's reality can be misleading and distracting from the importance of their delusion in making a diagnostic decision.
hidden decisions: Meehl identifies the decisions we make about patients that we do not explicitly own up to and do not often challenge. For example, placing middle- and upper-class patients in long term therapy, while lower-class patients are more likely to be medicated. This is related to the implicit ideal patient—young, attractive, verbal, intelligent, and successful (termed YAVIS)—that we would much rather have in psychotherapy, in part because they can pay for it long term and in part because they are potentially more enjoyable to interact with.
the spun-glass theory of the mind: The belief that the human organism is so fragile that minor negative events, such as criticism, rejection, or failure, are bound to cause major trauma to the system. Essentially not giving humans, and sometimes patients, enough credit for their resilience and ability to recover.[7]