I am a PhD student in the field of Applied Cat/Dog Technology*. I recently conducted an interview study with Cat and Dog owners. To analyse the interviews, I used and developed a theoretical framework invented by a semi-prominent professor in the field, let's call them C. Dogson. Using the analysis output, I have finalised a first draft of a journal paper detailing the interview study and improvement of Dogson's framework. Since I'm swamped with other work, I won't have time to submit the journal paper for about a month. Also, Dogson joined a recent seminar of mine and seemed very engaged in my work and eager to collaborate. Thus, I thought it might be a good opportunity to invite Dogson to read the journal article draft and potentially join as a co-author if they feel they can contribute substantially to the article before submission. I could see several benefits:
- The paper might meaningfully improve if they felt they had something to add
- They would help spreading the research in their context which is in another country
- It would teach me to manage international research collaborations
- It could lead to further collaboration e.g. a research exchange
- (Somewhat cynically) it seems like a natural career step to not only co-publish with my supervisors but add further co-authors to show proficiency in collaboration
With all these possible benefits in mind, I breached this idea to my supervisor. To my surprise, they rejected the idea, proposing that I do not invite Dogson as a co-author but instead try to publish alone and notify them after publication. Their argument was that inviting co-authors might "water down" the value of the research (which I do not entirely understand). They further argued that since Dogson is not an expert in the application of Cat/Dog technology but rather an expert on the Cat/Dog technology itself, their perspective on the interviews is probably not very useful.
I am not planning to go against my supervisors' advice, but I'd like to know if Academia.SE can put an end to the bad gut feeling I have about all this.
Considering this, I arrive at the following question: what are the potential drawbacks of inviting a researcher in my field as a journal paper co-author if they have expressed interest in collaboration and might provide a meaningful improvement to the research output? What might my supervisor mean by "watering down" the research by adding further collaborators?
*Field name censored for privacy reasons