Tips for More Effective Technical Writing

Tip #10 Numbers

Guideline #1: NEVER begin a sentence with a numeral.
Action: Choice 1—reword the sentence if you want to retain the arabic numeral, or
Choice 2—spell out the number.
Caveat: Always follow the guidelines of a designated style manual or those of the journal you are submitting a manuscript to for possible publication of your research.
Incorrect 66% of the people who responded to our e-mail survey have some college education, so nearly two-thirds of all Americans have some college education.
Correct
(reworded)
Of the people who responded to our e-mail survey 66% have some college education, so nearly two-thirds of all Americans have some college education.
Correct
(spelled out)
Sixty-six percent of the people who responded to our e-mail survey have some college education, so nearly two-thirds of all Americans have some college education.

Incorrect 70% of Madagascar's population live in extreme poverty and are mostly subsistence farmers.
Correct
(reworded)
Of its Madagascar's population 70% live in extreme poverty and are mostly subsistence farmers.
Correct
(spelled out)
Seventy percent of its Madagascar's population live in extreme poverty and are mostly subsistence farmers.

Guideline #2: If your writing includes much numerical data, then spell out only single-digit numbers and use numerals for everything else.
Purpose: avoid confusion and improve the likelihood of better understanding.
Original 1 This survey of 24 administrative districts over 3 years included 2575 participants.
Preferred This survey of 24 administrative districts over three years included 2575 participants.

Original 2 The car hit the wall at 80 kph and skidded for 9 feet.
Preferred The car hit the wall at 80 kph and skidded for nine feet.

Guideline #3: When numbers are used in a series, generally Arabic numbers are used for all numbers regardless of Guideline #2.
Incorrect 9 students of the group surveyed had studied French and 142 (students) had studied Spanish for three years or more.
Correct
(reworded)
Of the group surveyed, 9 students had studied French and 142 had studied Spanish for three years or more.
("9" and "142" are part of a series; "three" is not part of the series, so it is spelled out according to Guideline #2.)

Original 1 We analyzed 62 cases; of these, 59 had occurred in adults and three in children.
Preferred We analyzed 62 cases; of these, 59 had occurred in adults and 3 in children.
("3" is part of the series [59+3=62], so it is not spelled out according to Guideline #3.)

Guideline #4: When two numbers are adjacent (next to each other), spell one out and leave the other as a numeral. However, always use numerals with units of measurement
Incorrect 1
Incorrect 2
The sample was divided into 8 fifty-gram specimens.
The sample was divided into 8 50-gram specimens.
Correct
(reworded)
The sample was divided into eight 50-gram specimens.

Guideline #5: Leave 1 space after a number before a unit of measurement; 1 space before and after an equal "=" symbol and after the percent "%" symbol.
Incorrect X=2 A+Y=3.2X
Correct X = 2 A + Y = 3.2X

Guideline #6: Always use a "0" before the decimal point for numbers less than zero.
Incorrect 5m 32gm 520km P=0.05 .497 P =.05
Correct 5 m 32 gm 520 km P = 0.05 0.497 P = 0.05
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