Check numbers in a nonfiction manuscript

Check what the number means

“The survey involved 240 people” sounds precise, but precision is not the same as completeness. Were 240 people invited, interviewed or included in the final analysis? Before checking arithmetic, identify what each important figure counts. Keep that definition attached to the source note.

Numbers can survive a revision while their meaning changes. A paragraph about households becomes a paragraph about residents, but the total remains untouched. A figure originally described as annual is placed beside a monthly amount. Read the noun, unit and time period with the digits, not as separate copyediting details.

Create a short list of consequential figures: quantities central to the argument, prices used in comparisons, percentages, dates and worked examples. For each, record the source location and the version or date you used. Check the original source where possible rather than another article repeating the number.

Recalculate the worked example

Suppose a draft says a group grew from 80 members to 100, an increase of 25 per cent. Subtracting gives 20, and dividing that change by the starting figure gives the percentage increase. A later edit that changes the starting group to 75 requires a new calculation. Searching for “25” will not necessarily identify the dependency.

Reproduce calculations independently, with intermediate steps visible. Use a calculator or spreadsheet, then estimate the answer to check its scale. A plausible-looking spreadsheet result can still refer to the wrong cell. For a table, confirm totals and explain any rounding that prevents displayed parts from adding exactly to the displayed whole.

Distinguish a percentage change from a change in percentage points. Moving from 10 per cent to 15 per cent is a rise of five percentage points. The relative increase is different. Choose the description that answers the reader’s question, and make its basis explicit.

Compare repeated figures across the chapter, captions, tables and summary. A corrected number in the main paragraph may still be wrong in the introduction. Search distinctive values and associated terms, then inspect each occurrence rather than replacing blindly.

For estimates, preserve the uncertainty. Rounding an approximate measurement to several decimal places creates an impression the evidence does not support. Conversely, rounding too early in a calculation can distort the final result. Retain enough precision in the working, then choose a display appropriate to the source and purpose.

Leave an audit trail for any change that affects the argument. “Updated total from source table, checked against the stated period” gives an editor something to verify. If the corrected figure weakens the point, revise the point. The aim is a sentence that remains true when somebody follows the arithmetic.