How We Check Facts

1. We start from the source

We begin with whoever collected the data: government agencies, official datasets, published research and the organizations that keep the records. When we cite a news story or another secondary source, we say so, and we use it to find or explain the original, not to replace it. On new and rewritten pages, each source is listed with the date we last opened it.

2. Every new page has a claims table

Before a new or rewritten page is published, every number and factual claim in it goes into a working table. Each row records the source, the exact figure or wording, and what kind of claim it is:

• Fact: stated directly by the source.
• Our arithmetic: a figure we calculated from sourced numbers, with the calculation shown.
• Inference: a conclusion we draw from the evidence, written so it reads as ours.
• Unknown: something the sources do not settle. We say that on the page instead of guessing.

If a claim cannot be traced to a row in the table, it does not go on the page. When a page has a chart, the chart is built from the same figures.

3. A separate check before anything goes live

Writing a page and checking it are separate steps, and the writing step never signs off its own work. The check opens each source, compares every claim with its row in the table and reruns every calculation. On pages with a chart, it also confirms that the chart, its labels and its alt text match the text and the sources.

The check ends in pass, revise with the specific lines to fix, or fail. Our rule is that nothing is published without a pass. When a page changes, the changed lines go back through the check.

4. The words can’t say more than the evidence

A number can be right while the sentence around it says too much, so the check reads the wording as closely as the figures. A floor stays a floor: if a source says “at least,” so do we. A figure keeps its place, years and unit, and an average is not called typical. A link in the data is not written up as a cause. If we could not find something, we say “we found no,” not “there is no.” Our own calculations and conclusions are labeled as ours, never passed off as the source’s.

5. We check again after publishing

Once a page is live, we check the live version again against the text that passed. We have also reread published pages for claims that say too much, and some of our corrections started that way.

Many of our answers come from data that is updated each year. Each new or rewritten page shows the date it was last checked. When we find that a newer release changes an answer, we update the page, and we move the date only after we have re-confirmed the sources.

6. Corrections are dated and visible

If you think we got something wrong, write to hello@bookofodds.com and tell us the page and the claim. We will check it against the source. If we were wrong, we fix the page and add a dated note near the end of it, in this form:

Correction, <Month D, YYYY>: <what was wrong, and what the page says now>

We do not quietly rewrite a mistake. Spelling and formatting fixes don’t get a note.

When we rewrite an older page, we add a What changed note that lists the old figures the rewrite replaced, wherever we can confirm what the old page said. Some pages we rewrote in October 2026 do not have this note yet, and we are adding it.

What this is not

This is not expert review. Our health pages report what published data says, and they are not medical advice.

For how we think about odds, sources and uncertainty in general, see our methodology.

We use AI tools to help research, draft and check our pages. On pages we have checked, every claim matches a source you can open and every calculation has been rerun.