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., 1^st, 3^rd, 9^th).
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 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.