The sixth edition of the Publication Manual of the American Psychological Association presents guidelines for style and format when writing in the social or behavioral sciences. The text discusses aspects of grammar, including verb tense. The type of tense used depends upon the context of the situation being addressed.
Present Tense
If the introduction of the piece discusses any present-day issues, you may use present tense, such as "Students today are reading...." In addition, APA style also recommends the use of present tense in the conclusions section of a study. With this method, you draw in readers and engage them in considering the current implications of the research; for example: "The long-term effects are not yet understood, but...."
Past Tense
During a literature review, the discussion concerns the previous work of others. Therefore, APA style requires the use of past tense when relating research that occurred at a specific time in the past; for example: "Smith (2002) found that...." Along the same lines, when presenting your own procedures and results, use the past tense, such as "The participants completed the test...."
Present Perfect Tense
If the discussion involves past actions that do not have a definitive date, then you should use the present perfect tense, such as: "Institutional review boards have included outsiders...." In addition, if an action began in the past but continues into the present, use the present perfect tense; for instance: "Researchers have been studying the phenomenon...."