How is the criteria set out for one of the requirments of a PhD, adding to 'current knowledge'? Is it simply publishing a paper? We all know there are reputable journal, and not so reputable. Where is the benchmark by which we are all assessed?

I would presume that the requirement is to conduct research which is both original, and shows something which wasn't known before you started the project. Of course, there are different levels of originality, and different values of new knowledge, but considering that the percentage of PhD students who publish in a top-rated journal such as Science or Nature (or their equivalents), or more sepcific but still hightly-rated journals, is certainly not 100%, it is clear that you don;t have to make a ground-breaking discovery.

Indeed, the PhD is research training - if you were able to get published in superb journals all the time, there'd be no point doing a PhD and subsequent training, would there?

'Adding to Current Knowledge' can mean anything from discovering a new subatomic particle or a cure for cancer, to reinterpting someone elses dataset using a different analysis method; both are just as valid.

As for publishing; there are probably a large percentage of students that don't publish a paper at all. I think it's good to publish, especially if you want an academic career, but don't get too hung up on it and consider yourself a failure if you don't.

Indeed, Matthew is right when he says it's only training, and just one step on a very long career ladder...

Yes I totally agree. Howver, what has made me ask is that I was told that someone managed to obtain a PhD by conducting a variety of expts, all taken from other peoples reseach & analysed them in the same way. This is obviously quite obscure as we dont know the full details but all I can think is the but interpretation was differnet/original?