Written statements by potential witnesses or parties typically have a lower probative value than oral evidence taken by the department deciding on the case. If a disputed point is highly relevant to the validity of the contested patent, it is, as a rule, not in keeping with good procedural practice for an opposition division not to take up an opportunity to hear a witness or party in evidence and instead to require written statements and make do with their typically lower probative value. The board in T 329/02 could not identify any extraordinary circumstances that might have justified an exception to this rule in the case in point.
In T 918/11 the board found that it went against the general rules concerning the consideration of evidence to distinguish dogmatically between the evidentiary value of a witness testimony on the one hand and a document on the other hand. The opposition division had apparently considered documents to be of a more conclusive evidentiary value than witnesses. Such an approach had no basis in the EPC, Art. 117 EPC containing no ranking of the means of evidence it listed (see also T 2565/11, in which it was similarly found that witness testimony and documents were not ranked in this way).