According to the sixth edition of the "Publication Manual of the American Psychological Association" and the seventh edition of the "MLA Handbook for Writers of Research Papers," writers using either the APA or MLA documentation format should avoid using titles such as "Ph.D." by authors' names in the citations or references pages. However, these style guides, along with the 16th edition of "The Chicago Manual of Style" and AP style, do allow the use of such titles at the end of names in the text, when needed.
In Chicago and MLA style, a Ph.D. title is not included in the references, but it can be included in the text. In that case, the doctoral degree title at the end of a name appears after a comma but with no punctuation within the letters in the degree and both the "P" and the "D" should be capitalized. For example: Steven Hammersmith, PhD. AP style also does not cite the degree in the references, and it prefers a phrase instead of an abbreviation in the text, when possible. For example: Jane Doe, who has a doctorate in chemistry. When the preferred style is too cumbersome, such as when several people and their titles need to be identified, AP style requires a period between the two portions of the abbreviation: Ph.D. The capitalization remains the same as in Chicago, however, as does the requirement for the comma between the name and the title. APA is similar to AP style, with a period between the two portions of the abbreviation, and it also does not include the academic degree in the references.