Essentially one is limited to (1) relatively vague journals' instructions to reviewers usually on the lines of "be constructive" or "be charitable", (2) deducing what matters to the editor from the questions asked in the reviewer's report form, and (3) emulating the style of the comments one receives on one's own papers. Apart from generic, often system-generated thank you messages there is generally no feedback on whether and to what degree the editors found my reviewer's reports appropriate and helpful or on how they compared with other reports.
In other words, most of it is learning by doing; after years of practice I now have a good overview of what reviewer reports in my field look like, but as a beginner I had very little to go by.
It is then no surprise that the style and tone in which reviewers in my field write their reports can differ quite a lot from person to person. There is a general pattern of first discussing general issues and broad suggestions and then minor suggestions line-by-line on phrasing, word choice or typos, and there is clearly the expectation of being reasonable and civil. But:
- Some reviewers may summarise the manuscript abstract-style before they start their evaluation, while others assume that the editor does not need that information given that they have the actual abstract of the paper available to them.
- Some stick to evaluating the scientific accuracy of the paper, while others obsess about wording and phrasing and regularly ask authors who are native speakers of English to have a native speaker of English check their manuscript.
- Some stick to judging whether the analysis chosen by the authors is suitable to answer the study question, while others see an opportunity to suggest the addition of five totally irrelevant analyses just because they happen to know they are possible. And sometimes they recommend cutting another 2,000 words from the text despite suggesting those additions, as if those would come without text.
- Some unashamedly use the reviewer's report for self-promotion by suggesting that some of their own publications be cited, relevant or not.
- Some use a professional tone and make constructive suggestions on the particular manuscript in question, but others apparently cannot help disparaging the authors themselves. Luckily that behaviour is rare.
- Some write one paragraph even when they recommend major revision (meaning they could have been more explicit about what and how to revise), others write six pages of suggestions even when their recommendation is rather positive.
First, I like to print the manuscript - I am old-fashioned like that. I try to begin reading it fairly soon after I accept the job, and for obvious reasons I also try to read through more or less over one day. Often I will read when I need a break from some other task like computer work, on a bus or in the evening at home.
Already on the first read I attempt to thoroughly mark everything I notice. Using a red or blue pen I mark minor issues a bit like a teacher correcting a dictation, while making little notes on the margins where I have more general concerns ("poorly explained", "circular", "what about geographic outliers?").
Usually the following day I order my thoughts on the manuscript and start a very rough report draft by first typing out all the minor suggestions. (I would prefer to use tracked changes on a Word document for that, but unfortunately we generally only get a PDF, and I find annotating those even more tedious than just writing things out.) Then I start on the general concerns, if any, merely by writing single sentences on each point but do not expand just then.
In particular if the study is valuable but has some weaknesses I prefer to sleep over it at this stage for 2-3 nights or, if the task has turned out to be a bit unpleasant, even a few days more, and then look at it again with fresh eyes. That helps me to avoid being overly negative; in fact I tend to start out rather bluntly and then, with some distance, rephrase and expand my comments to be more polite and constructive.
That being said, if the manuscript is nearly flawless or totally unsalvageable I usually finish my review very quickly. If I remember correctly my record is something like 45 min after being invited to review, because the study was just that deeply flawed. In that case I saw no reason to spend a lot of time on trying to develop a list of minor suggestions.
More generally I have over the years come to the conclusion that it cannot be the role of a peer reviewer to check if all papers in the reference list have really been cited or to suggest language corrections in each paragraph, although some colleagues seem to get a kick out of that. If there are more than a handful of language issues I would simply say that the language needs work instead of pointing out each instance, and if there are issues with the references I would suggest the authors consider using a reference manager such as Zotero, done. Really from my perspective the point of peer review is to check if the science is sound, and everything else is at best a distant secondary concern.
At any rate, after having slept over the manuscript a bit I will return to it and write the general comments out into more fluent text. I aim to do the usual sandwich: start with a positive paragraph that summarises the main contribution made by the manuscript and what I particularly like about it. If necessary, this is followed by something to the effect of "nonetheless I have some concerns" or "unfortunately, some changes are required before this useful contribution can be published".
Then comes the major stuff that I would suggest to change, delete or add, including in each case with a concrete recommendation of what could be done to improve the manuscript. I follow a logical order through the text but usually end with what I consider most important, or repeat that point if it was already covered earlier. To end the general comments on something positive I will have another paragraph stressing how valuable the manuscript would be, that I hope it will ultimately be published, etc. Even if I feel I have to suggest rejection I try to stress a positive element of the work.
Finally, and as mentioned above, there is the list of minor suggestions. Most other reviewers I have run into seem to structure their reports similarly.
When submitting the report, however, one does not only have to provide the text I have discussed so far, although it is certainly the most useful from the authors' perspective. No, nearly all journals have a field of "reviewer blind comments to the editor", which I rarely find necessary to use, and a number of questions that the reviewer has to answer. The latter are typically on the following lines:
- Is the language acceptable or is revision required?
- Are the conclusions sound and do they follow logically from the results?
- Are all the tables and figures necessary?