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Research Style & Usage: APA/MLA


APA Style: Statistics, Math, and Measurements



  • Always use the metric system. If the original study was conducted using non-metric units, provide the original units followed by metric conversions in parentheses.



  • In general, use words for numbers below 10 and numerals for numbers 10 or above.

  • However, always use numerals for:

    • Numbers below 10 when grouped with numbers above 10: 6 of 32 trials

    • Numbers that precede units of measurement: 5 cm.

    • Numbers in a list of four or more numbers: 3 women, 6 men, 11 dogs, 9 bees

    • Statistical or mathematical functions, percentages, ratios, and decimal amounts: 8% of those interviewed

    • Numbers that represent time, money, scores on a scale, or numbers of participants: $5

    • Names of books or tables: Chapter 4, Table 7

  • Always use words instead of numerals to begin a sentence: “Twelve trials revealed . . .”

  • Put a zero before the decimal point in a fraction unless the fraction never can be greater than one (e.g., a correlation or probability): 0.78 mm, p=.78

  • Two decimal places are usually enough.

  • Make plurals of numerals by adding an s without an apostrophe: 1950s


Statistical Symbols

  • Lowercase Greek letters are used for population statistics (also known as parameters).

  • Italicized Latin letters are used for most sample statistics.

  • Italicize all statistical symbols except for vector symbols, which should be typed in bold, and Greek letters, subscripts, and superscripts, which should remain in the standard font.

  • Use an uppercase italicized N for the total number of participants; use a lowercase italicized n for subsets of participants: N=180, n=15

  • Use parentheses to identify degrees of freedom and sample size in a chi-square test.


Mathematical Equations and Formulas

  • Space and punctuate equations and formulas as you would regular words:

    • In the equation 3x + y = z, we see that . . .

  • Put simple equations in the text.

  • Set off complicated equations from the text with two double spaces above and below, numbered in the right-hand margin with an Arabic numeral in parentheses.

  • Layer parentheses as follows: ( ) first, then [ ], and finally { }.

  • When placing symbols next to a variable, prime marks come before subscripts, which (generally) come before superscripts.