The decision of Bennett J in Inverness Medical Switzerland GmbH v MDS Diagnostics Pty Limited  FCA 108 highlights the importance of expert witnesses being truly representative of the hypothetical person skilled in the art.
Inverness relied on the evidence of Boscato, “a person who works at a bench in a laboratory rather than being a theoretical researcher. She has designed and made immunoassays, uses them routinely and has a “practical interest” in the subject matter of the invention.” By comparison, MDS relied on the evidence of Sinosich, a person who “has worked in the field of immunoassay development, including immunoassays for a range of fertility, pregnancy and non-pregnancy associated analytes. He has generated both polyclonal and monoclonal antibodies; all of his research activity has been antibody-based.”
A significant issue in the case was the construction to be given to the expression “specific binding reagent” as used in the claims of the patent. Sinosich considered that the adjective “specific” used in relation to a reagent was a term of art meaning that the reagent would preferentially bind to an analyte in the immunoassay with no binding to any other molecule in the sample. Boscato agreed that, in the context of immunoassays, “specificity” meant the ability to measure the analyte without interference from other substances which would cause a false positive response, or interference from other substances causing an inaccurate result but that there was a distinction between the use of “specificity” and “specific”. Boscato considered that the use of “specific” in the phrase “a specific binding reagent for an analyte” meant that the reagent has to be able to bind the analyte of interest in a specific binding reaction, but not necessarily exclusively.
In relation to the difference in interpretation between the two expert witnesses, Bennet J commented that:
I formed the clear impression that, while Dr Sinosich gave his opinion honestly and impartially, his approach was, as he conceded in evidence, influenced by his own specific area of expertise and his own rigorous approach to the relevant terminology. It was apparent during cross-examination when Dr Sinosich was taken to different parts of the specification that the patentee did not adopt the same limited use of terminology.
Another important consideration in determining the correct construction, as noted by her Honour, was that Sinosich’s construction did not accord with much of the literature as at the priority date, or with the specification, which has broader application. By comparison, Boscato pointed to literature which formed part of the prior art, including papers considered to be very important in the field at the priority date, which showed use of the expression “specific binding reagent” consistent with her construction. Bennet J concluded that:
Dr Sinosich’s use of the terminology may well reflect his own experience and practice but the evidence suggests that it is not and was not the common use of others in the art to which the specification relates.
This decision highlights the importance of carefully selecting expert witnesses but also the importance of contemporaneous documentary evidence in supporting the views expressed by those witnesses.