Harvard Referencing method: When a source has three or up to seven authors the first author is mentioned in the text, followed by et al. in italics (note the full stop only at the end of et al. as it is an abbreviation for et alii, meaning and others).
APA Referencing method: When a source has three or more authors, mention the first author in the text, followed by “et al.” in every citation (even the first citation). This is followed by the date.
