What to change between Conference and Journal Paper?

Question

If one is extending work previously published in conference proceedings, what must be changed?

Specifically, does one need to change the Introduction, Background Work, or similar sections that are not actually the new material being presented?

I understand that some journals use a plagiarism detection system that would throw serious red flags if sections were untouched; so, how do editors view this?

It seems reasonable to not have to modify every sentence, especially where the material has not changed.

Thoughts?

Edit: Typically, 25-30% new material should be presented, but does this have to come at the cost of rewriting some portions of the work that remain the same?

Answer 1

There is no good reason to simply copy large portions of an existing publication to make a new. By rewriting everything, you have the opportunity to rephrase your thoughts and most likely produce a better paper, at least from a writing point of view. Some journals definietly look at plagiarism and in this case self-plagiarism and the only way to avoid it is to rewrite. I think the benefits of rewriting clearly outweighs the possible time-saving by just copy-pasting.

Just to provide an example. I have written tens of papers about the same natural physical object that I have studied. In each paper, I have to provide a descritpion of the locality and characteristics and not once have this been copied. It is in fact interesting to see how many dofferent ways the same (dull) information can be conveyed.

As for a percentage of new material, I really would advice against relying on a numbr. It is possible this is a silent understanding in some fields but in general, only new insights and conclusion should warrant a new publication. Another year of data or something similar to that is in itself not enough. The paper might be published but such publication strategies are not looked upon favourably in the long term.

So, I strongly recomend rewriting each paper and not rely on copy-pasting. I am convinced you will develop as an author and also generate better papers by doing so. consider each paper a separate new entity.

Answer 2

I agree with @Peter Jansson, and I believe there is significant reason to rewrite the paper. That said, some of it is simply tedious!

I'm just going to add an answer here that I received after reaching out to an editor about this question.

Summary of their response:

Good question! I will give you my point-of-view as an editor:

• The delta will be evaluated semantically not textually.
• There is no definitive need to rewrite sections; however, since you are not subject to the same limitations as a conference paper, detailed explanations are highly welcomed, specifically in unclear or shortened sections.
• Also, since an extended paper contains something new, it is unlikely that Intro and Conclusions will be the same, and changes should be made accordingly.

Answer 3

Quite likely, when you were writing the conference version of the paper, you found yourself having to compress and cut here and there, ultimately telling a different story than the one you would have liked to tell. These cut will have occurred throughout the entire paper. When writing the journal version of the paper, you will have the chance to expand on those previously compressed sections. Indeed, you probably have better ways of explaining things or new insights. Now is the time to give those explanations and insights.