# Numbers

• GN01: We must not put numbers in parentheses after they have already been mentioned (e.g., five (5)).

• GN02: We must use words to express numbers below 10, unless the numbers precede a unit of measurement (e.g., 4.52 cm), they are part of statistical or mathematical operations (e.g., 5% of the participants; divided by 8), or they denote dates, exact amounts of money, specific places in numbered series, parts of books and tables, or each number in a list of four or more digits.

• GN03: We must express in words numbers at the beginning of a sentence or a title (e.g., Fourteen participants were in the control group) and common fractions and phrases (e.g., Three-fourths of the population).

• GN04: We must separate the integer parts of decimal numbers from their fractional parts using decimal points, not commas.

• GN05: We must place a zero before a decimal fraction less than 1 if the statistic can exceed 1 (e.g., 0.49 in); otherwise, the zero is not necessary (e.g., p = .93).

• GN06: For numbers over 1,000, we must use the comma to separate groups of three digits except for page numbers, binary code, serial numbers, temperatures, acoustic frequencies and degrees of freedom.

• GN07: We must not add apostrophes when we write a plural of a number (e.g., the 90's).

• GN08: When one number follows another in a sentence, we should mix numbers with words (e.g., 4 three-year-old dogs), but, in some cases, the wording may be modified for clarity.

• GN09: We must not use the superscript for ordinal numbers (e.g., 1st, 3rd, 9th).

• GN10: When we are presenting values with decimal numbers in a text, we must not give the values of the same variable with a different number of decimals.

• GN11: We must use words instead of mathematical symbols (e.g., plus, equal) in narrative texts.

• GN12: We must use spaces between elements in mathematical expressions to facilitate reading (e.g., a × -b = c; here, the minus sign is not separated from the b because it represents its negative value).

• GN13: When we talk about monetary values of millions and billions, we should use the abbreviations M and B, respectively (e.g., \$15.4M). We must not express the whole number unless strictly necessary, for example, for some kind of analysis.