Curr Allergy Asthma Rep (2012) 12:590–598 Fig. 1 Differential diagnosis versus causation analysis 593 establish and testify to the probability of that causal attribu- tion. Recognizing this dichotomy between diagnosis and causal assessment, some courts have defined the processes more like the one illustrated in Fig. 1 and called these separate analyses “differential diagnosis” and “differential etiology,” another name for causation assessment. While it is indisputably true that the result of the differential diagnostic process quite properly leads physicians to a clinical diagnosis, it is certainly not the case, except in rare instances, that it leads to causal conclusion. Even for allergists, there are two processes. First, the allergist must determine whether the red eyes are the result of irritation, infection, or allergy. Once allergy becomes the diagnosis, only then can the etiology (which allergen?) be sought and established. Analyzing the Exposure Source Identifying the source of the exposure is probably the most vexing issue of all the causal questions which arise in a lawsuit. Allergists are more attuned than most specialists to this concept. They often need to provide allergy-mitigation recommendations which can lead to generic protection by, say, bed covers to reduce the load of dust mites. However, in the context of a claim in which a roof leak is linked by the patient or his/her lawyer to respiratory aller- gies, the allergist must demonstrate an intense investigation of the source of the allergen in order to establish a legally acceptable causal conclusion. Often the allergist will accept the patient’s attribution, converting and transforming the patient’s perceived cause to a medically espoused and rati- fied one. The patient said: “My symptoms started with the roof leak and mold grew in the house; therefore, mold in the house from the roof leak caused my illness.” However, before the allergist can testify to such a causal attribution, he/she must anticipate and consider how the questioning by the opposing attorney will proceed: “How long did the roof leak and how much water damage was there?” “How much mold grew and where was it?” “What genera and species of mold were found in the air?” “How large an area did the mold cover?” “How representative of the entire living space was the swab sample you reviewed?” “If you are claim- ing that this was a ‘wet/damp’ space, how wet was it and how much space was wet and damp?” and “Did you review the indoor air evaluation reports or perform a site visit?” These are only a few of the reasonable questions that will likely be asked of a physician or any other expert who links a source, in this case a roof leak, that allegedly led to mold growth that alleg- edly led to a clinical outcome. Patient/Claimant and Physician Confounders It is not unusual for patients visiting the allergist to come with some idea of the “cause” of their problems, whether it is a specific food, seasonal outdoor allergens, a damp home, workplace, perfume, or other environmental irritants. It is a near certainty that, if a legal claim has prompted the visit to the allergist’s office, the patient will think he or she “knows” the cause of his/her complaints. It is also a given that a refutation of a patient’s causal attribution, if not confirmed by clinical evaluation, is more readily accepted by the patient who is not a claimant than by one who is. The latter, after all, is driven by two impulses—to get medical help and to succeed in a pursuit of the claim. The patient’s suspicions about the cause of his or her illness, combined with the desire to hold someone liable for causing that problem, inevitably leads to certain reporting biases, whether intentional or subconscious, which com- monly color the clinical history. Another bias in claims- related matters is a form of attribution bias which comes from fear or worry about environmental hazards. For