71 PRS Proofreading and Editing Service PhD Experts • All Academic Areas • Fast Turnaround • High Quality full stop and italics are not required, but when to use ‘et al.’ is a little more complicated. If a source has three to five authors, all authors should be listed for the first citation in a paper (Thompson, Smith, Jones, & Johnson, 2008), but all subsequent in-text references should use the first author’s name followed by ‘et al.’ (Thompson et al., 2008), so special care needs to be taken to ensure that each citation appears in the correct format. For six or more authors, APA style uses ‘et al.’ after the first author’s name in all references to the source, including the first one (on the use of ‘et al.,’ see also Section 4.2). If you find that you use in your paper two or more sources with the same date and by the same author (or authors), you’ll need to add a lowercase letter to each date regardless of which author-date referencing system you’re using (Smith, 2010a, 2010b; Thompson et al., 2008a). You will need to add these letters to the dates of the same sources in your reference list as well so that your in-text references successfully lead your readers to the right source in every case. In fact, everything about the author and date information provided in in-text citations within a paper must correspond exactly to the same information in the accompanying reference list, so author names and dates should be carefully compared between the paper and list to ensure absolute accuracy. Finally, your parenthetical citations should also be appropriately positioned in relation to the punctuation of your sentences, generally before any punctuation marks: e.g., ‘According to Smith (2010a), there was…’ and ‘…just as a recent study has shown (Smith, 2012).’ In a numerical system of referencing such as that required by Vancouver style and the guidelines of a number of journals that call for variations on the Vancouver system, each source used is assigned an Arabic (rarely a Roman) numeral and that same number is used every time the same source is cited in a paper. The sources PARt II: PRePARIng, PResentIng And PolIsHIng YoUR woRk