APA Style & Citation 7th edition

Use words to express numbers under 10. Use numerals to express numbers 10 and above.

Also use numerals:

• in your abstract
• in measurements (5 cm)
• in mathematical functions (multiplied by 5; 3 times as many; 5% of the sample)
• when expressing time, dates, ages, scores, sums of money

Use words:

• when numbers appear at the beginning of a sentence
• in fractions (one fifth of the class)
• for universally accepted usages (the Twelve Apostles)

Never use an apostrophe when expressing numbers in plural form (in the 1970s; 10s and 20s).

Capitalize:

• The first word in a sentence, even if it would normally be lower case
• Titles: capitalize every major word
• Proper nouns, including:
  • brand name drugs (not generic names)
  • names of specific departments (Department of Graduate Studies)
  • nouns followed by numbers or letters (Day 2, Figure 3B)
    • but not nouns followed by a variable (trial n)

Italicize:

• titles of:
  • books
  • journals
  • movies
  • TV shows
• a new key term, but only the first time used
• words and letters used as examples (the letter a)
• variables/statistical symbols

Avoid using italics for emphasis. See section 6.22 of the Publication Manual of the American Psychological Association (7th ed.) for full list or instances to use italics.