When dealing with a manuscript I comprehended that my co-authors and myself have to read, update, expand, correct the manuscript for about 40 times before it is sent to the journal. Plus a statistician should be included. Plus proofreading. This number is let’s say final and this number can be divided to the number of co-authors. Probably this partly depends on the organization of writing/publishing from institution to institution. The number is an estimate for the publication in a journal indexed in Current Contents.