An alphanumeric outline uses Roman numerals, capitalized letters, Arabic numerals and lowercase letters as prefix headings.
The Chicago Manual of Style (CMS) uses the following outline format:
I. (Roman numeral)
A. (Capital letter)
a) (Lowercase letter followed by closing parenthesis)
(1) (Number enclosed in parenthesis)
(a) (Lowercase letter enclosed in parenthesis)
i) (Roman numeral with lowercase letters followed by a closing parenthesis)
The Modern Language Association (MLA) uses essentially the same method except the first lowercase letter is followed by a period instead of a closing parenthesis.
The decimal outline uses only numbers as prefix headings making it easier to see how every item relates within the hierarchy. It uses the following outline format:
Here is a sample decimal outline:
1.0 Choose Desired College
1.1 Visit and evaluate college campuses
1.2 Visit and evaluate college websites
1.2.1 Look for interesting classes
1.2.2 Note important statistics