- Level 1: Centered all capital letters. Use this level for major sections of text such as Materials and Methods and the Discussion.
- Level 2: Freestanding flush-left boldface. Use this level only to group two or more closely related Level 3 headings in long article.
- Level 3: Paragraph-initiating boldface followed by a colon.
- Level 4: Paragraph-initiating italic. Level 4 headings may be numbered but only when the numbers must be cited in the text.