APA Style: Statistics, Math, and Measurements

 

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.

 

Numbers

• 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.