I often see them in the middle of the sentence and sometimes at the end, as a collective. I am wondering is there a rule for this type of citation. Is it personal preference or journal specific?
Each journal will state its specific citation style preference. Typically, most journals will have an "About" or "For Authors" link that explains their respective expectations for authors.
Each journal will state its specific citation style preference. Typically, most journals will have an "About" or "For Authors" link that explains their respective expectations for authors.
Citation style varies from Journal to Journal. Each Journal has specific citation which is generally mentioned in Author's Guidelines. Authors have to follow these guidelines.
Sometimes journals do not specify that you cite immediately after the specific fact being cited or at the end of the sentence. To me it feels misleading the reader if I cite a single fact in a sentence containing several facts from different sources at the end of a sentence.
For example: If I have taken two facts that Guava leaves contain antimicrobials from Mtewa 2017 and that Guava leaves contain antioxidants from Boyle, 2017. There are two possible ways to cite, now the question is which one is right if a journal 'instruction to author' is silent?
a) Guava leaves are reported to contain antimicrobials (Mtewa, 2017) and antioxidants (Boyle, 2017) giving them the value they posses in the field of herbal medicines.
b) Guava leaves are reported to contain antimicrobials and antioxidants giving them the value they posses in the field of herbal medicines (Boyle, 2017; Mtewa 2017).
To me, the second presentation (b) is quite misleading as it insinuates that both Mtewa and Boyle reported both properties and in addition, that the plant has value for such properties. Different from the original fact, well presented in example (a) above.