Legal Memorandum: Substantial Similarity Rule

Issue: Does the substantial similarity rule require a comparison of identical products?

Not all circumstances of the accident must be substantially similar; only the defect relevant to the alleged claim must be substantially similar.  See Smith v. Ingersoll-Rand Co., 214 F.3d 1235, 1248-49 (10th Cir. 2000) (“The substantial similarity rule does not require identical products; nor does it require us to compare the products in their entireties [rather] [t]he rule requires substantial similarity among the variables relevant to plaintiff’s theory of defect.”); Belliger v. Deere & Co., 881 F. Supp. 813, 818 (N.D.N.Y. 1995) (New York courts “define the similarity of the accidents based upon the product or defect at issue”); Fine v. Facet Aerospace Prods., Co., 133 F.R.D. 439, 441 (S.D.N.Y. 1990) (“different models of a product will be relevant if they share with the accident-causing model those characteristics pertinent to the legal issues raised in the litigation”).  On the other hand, “differences in the surrounding circumstances go to the weight to be given the evidence, rather than to its admissibility.”  Id.  Moreover, even if the evidence were not otherwise admissible, it may still provide the basis for expert testimony because it is “of a type reasonably relied upon by experts in the particular field.”  Fed. R. Evid. 703. 

Substantial likelihood of harm can be established by circumstantial evidence, without the need for expert testimony.  Arnold v. Krause, Inc., 233 F.R.D. 126, 130 (W.D.N.Y. 2005). 

Moreover, there is no requirement that expert testimony be based on the expert’s own underlying testing in every case.  Instead, “an […]