Researchers place brief parenthetical descriptions to acknowledge which parts of their paper reference particular sources. Generally, you want to provide the last name of the author and the specific page numbers of the source. If such information is already given in the body of the sentence, then exclude it from the parenthetical citation. Place the parenthetical citation where there is a pause in the sentence – normally before the end of a sentence or a comma. The in-text citation will differ depending on how much information you provide within the sentence.
Citation patterns are also known to be affected by unethical behavior of both the authors and journal staff. Such behavior is called impact factor boosting, and was reported to involve even the top-tier journals. Specifically the high-ranking journals of medical science, including the Lancet, JAMA and New England Journal of Medicine, are thought to be associated with such behavior, with up to 30% of citations to these journals being generated by commissioned opinion articles.  On the other hand, the phenomenon of citation cartels is rising. Citation cartels are defined as groups of authors that cite each other disproportionately more than they do other groups of authors who work on the same subject.