APA, the American Psychological Association, has specific rules about how you write APA-style manuscripts, including how to use italics. The "Publication Manual of the American Psychological Association" provides detailed guidelines for when and how to use italics. This publication also indicates when not to use italics.
Words used for species and varieties are italicized; for example "Macaca mulatta." Use italics to introduce a new term or one that is technical, such as "diffusion of responsibility." Only italicize the word or words the first time you use them in an article. Also, use italics for words or terms that you could misread or misunderstood. For example, if you use a stimulus photo of an old man, "old man" is italicized in the text.
Statistics and Tests
Letters used to indicate statistical symbols are always italicized. For example, the t in t-test, the F in F-test, df (degrees of freedom) and p (probability) are written in italics. You also italicize letters used as algebraic variables, as in "a = b (c + d)." You also italicize the sub scales in some psychological tests, such as the "Z" sub scale in the Rorschach test.
In the References section of an APA paper, the titles for journals, books, videos, TV shows and films are italicized, such as the "Journal of Personality." However, if a book title is part of the text that is italicized, use regular type. This is called reverse italicization. An example is "Understanding Wright’s" The Biology of Violence where Understanding Wright's is in italics, but The Biology of Violence is in regular type. The volume numbers for journals in the References are also italicized.
Other Uses for Italics
The designations of the end points of a scale are italicized; for example, responses varied from 1 ("strongly disagree") to 6 ("strongly agree"). The words in the parentheses are italicized. Words or phrases in a linguistic example are also italicized. For example, if you say the interpretation of “walked softly” was asked, walked softly is in italics.