It is a usual practise to use different styles for different research areas and fields of study. You should choose appropriate style for your thesis writing. There are a lot of formats for thesis writing, such as American Psychological Association (APA) Style, Modern Language Association (MLA) Style, Chicago style and so on.

Are You Having Problems Writing Your APA Thesis?
A thesis presents the research work done by an undergraduate or graduate student in his area of study. It is mostly written in two common styles, the APA or the MLA styles. The APA thesis writing, the more widely used format, is known as the American Psychological Association style. This is because the APA format and style is the writing style used by the various journals published by the American Psychological Association. It is usually used for works related to the social sciences. The APA thesis writing standard has been set forth in the American Psychological Association’s Publication Manual.
The APA thesis format consists of thesis writing specifications. The APA thesis sets out the standards for the formatting of the text, the arrangement and markup of the headings, tables and reference and citation lists. The Harvard referencing system is extensively used in APA thesis writing.
Very often, students find the writing of an APA thesis/dissertation to be quite problematic.
Use of headings: The APA format and style dictates that your print size has to be 12 and the font, Times New Roman or Courier. Most papers use at least three heading levels. The APA format and style for titles can prove quite confusing to use, and it is better for the student to check with his/her consultant.
Avoid biased language: When you are writing an APA thesis/dissertation, you have to avoid using biased language, or any language which may cause offense to someone. You are not to use ethnic labels like Hispanic, instead use geographical labels like Mexican American. Similarly, do not use words like “lesbians” or “gay men” instead of “homosexuals”.
The correct use of this style can be quite tricky and subjective. A consultant will be able to spot any use of biased language in your dissertation and he/she can rectify any incorrect use of language.
Capitalization: Most students find the APA capitalization style and format requirements confusing to follow. Use the following guidelines:

In thesis writing, citation is a must. Without it, nothing you say can be taken under serious consideration, and in fact, you will surely be docked points and even prosecuted for plagiarism if you do not properly cite your sources. In order to keep this from happening, Thesis Town presents this quick guide to APA thesis citation.

When it comes to thesis writing, lot of people have problems with the guidelines and requirements one must follow for an APA thesis. They are very different from the MLA and AP style and citation requirements, but not so drastically that it feels like an entirely new system.