APA Style is a “down” style, meaning that words are lowercase unless there is specific guidance to capitalize them. For example, capitalize the first word of a sentence, unless the sentence begins with the name of a person whose name starts with a lowercase letter.
The Publication Manual contains guidance on how to capitalize words beginning a sentence; proper nouns and trade names; job titles and positions; diseases, disorders, therapies, theories, and related terms; titles of works and headings within works; titles of tests and measures; nouns followed by numerals or letters; names of conditions or groups in an experiment; and names of study factors, variables, and effects. Only a subset of the guidance is presented on the website to answers users’ most common questions.
Capitalization is covered in the seventh edition APA Style manuals in the Publication Manual Chapter 6 and the Concise Guide Chapter 5
