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T 0555/18: Parametric Definitions And The Burden Of Proof – Patent


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Earlier this year, Stephan Schultes and Magnus Johnston took an in-depth look at the way the
European Patent Office (EPO) examines claims to inventions defined
in terms of parameters. They noted that while chemical and
materials related inventions often lend themselves to parametric
definitions in terms of physical structures and experimentally
measurable properties, such definitions can lead to problems with
clarity and sufficiency. In some cases, EPO examiners can consider
the use of parameters to be an attempt to disguise a lack of

A recent decision (T 0555/18) by a Technical Board of
Appeal at the EPO considered how inventive step is to be assessed
when the only distinguishing feature of the claim is an unusual

In this case, the claim related to a multilayer, heat-shrinkable
film defined inter alia in terms of a Fourier-transform
infrared (FTIR) spectroscopic transmission absorbance ratio to be
measured upon conditioning at a specified temperature and humidity
for a specified length of time. The patent explained that an
absorbance ratio of 1.65 or lower indicated a high polyamide
content, which conferred high strength, and a low degree of
crystallinity, which conferred high transparency.

The opponent as appellant argued that the FTIR transmission
absorbance ratio was an unusual parameter not commonly used in the
field, and the Board agreed.

According to the EPO’s Guidelines for Examination, there are
two types of unusual parameter:

(i) The unusual parameter measures a property of the
product/process for which another generally recognised parameter is
used in the field of the invention.

(ii) The unusual parameter measures a property of the
product/process that was not measured before in the field of the

Parameters which fall into class (i) are considered to be
prima facie objectionable on grounds of lack of clarity,
because no meaningful comparison can be made with the prior art, if
no straightforward conversion from the unusual parameter to a
parameter generally recognised in the art is possible, or if a
non-accessible apparatus for measuring the unusual parameter must
be used.

Parameters which fall into class (ii) are allowable if it is
evident from the application that the skilled person would face no
difficulty in carrying out the presented tests and would thereby be
able to establish the exact meaning of the parameter and make a
meaningful comparison with the prior art. However, the onus of
proof that an unusual parameter is a genuine distinctive feature
vis-à-vis the prior art lies with the applicant.

In T 0555/18, the Board considered that the FTIR transmission
absorbance ratio was the only distinguishing feature over prior art
document D3 and had to determine (a) whether a difference in this
parameter really led to improved optical properties and (b) whether
working in the claimed range would not be obvious based on a
combination of disclosures within D3, as the patent proprietor had

With regard to question (a), the Board was not convinced by the
proprietor’s arguments and concluded that the stated technical
effect was not achieved. The objective technical problem was
therefore merely the provision of an alternative film to the one
known from D3.

With regard to question (b), the Board noted that, when the only
distinguishing feature is a range of an unusual parameter, the
assessment of obviousness might be clouded by the fact that such
parameters are by definition rarely described in the relevant prior
art. This means that indirect comparisons between the claimed
parameter and estimates based on more common parameters in the
prior art could lead to uncertain conclusions. This opened the
question of who should bear the burden of proof as to whether or
not the resulting estimates are sufficient to render the invention

The Board then determined that the case law on unusual
parameters in the context of novelty had to be followed
when assessing inventive step, meaning that, in cases of
doubt, the burden of proof had to lie with the patent proprietor.
The Board considered this approach to be justified because it would
be unequitable for a party to benefit from the uncertainties
created by its decision to define the invention in terms of an
unusual parameter.

In the present case, the Board found that this burden of proof
had not been discharged by the proprietor because no evidence had
been provided to demonstrate that a film which would result from
combining the relevant disclosures in D3 would have an FTIR ratio
falling outside the claimed range. The claim was therefore found to
lack an inventive step.

This decision highlights the difficulties which may be
encountered when defining inventions in terms of unusual
parameters. As noted in our previous article, extreme care must be
taken when drafting applications of this nature, and the burden on
the proprietor to provide evidence substantiating the invention
continues even after grant.

The content of this article is intended to provide a general
guide to the subject matter. Specialist advice should be sought
about your specific circumstances.

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