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6.15

Self-reported vs measured numbers

Before you trust a number, find out whether people said it about themselves or someone measured or counted it.

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Photo: RDNE Stock project / Pexels
Area: InformationFrom age 15Time to learn: 15 minutes

You will tell survey answers people gave about themselves apart from data that was measured or counted, and know when the difference matters.

Why it matters

People forget, guess, and lean toward answers that make them look good. When a US national health survey measured activity with motion sensors in 2003 to 2004, fewer than 5% of adults met the 30-minutes-a-day guideline, a share far lower than people's own reports suggested (Troiano et al., NIH). Most numbers in the news are one kind or the other, and the label is often in small print.

How to do it

  1. Find how the number was collected. Look for a 'methods', 'about the data', or 'source' note, or the footnote under a chart.
  2. Look for self-report words: survey, poll, respondents, 'said', 'reported', 'say they'.
  3. Look for measured or counted words: measured, tested, recorded, sensor, lab test, records, registrations, death certificates, sales.
  4. Ask whether people have a reason to shade the truth. Weight, exercise, drinking, voting, income, and skills are often over- or under-reported.
  5. Ask whether people would even know. Few people know their exact screen time or blood pressure without measuring.
  6. Label the number when you repeat it: '55% say they have three months of savings', not '55% have three months of savings'.
  7. When both kinds exist, trust measured data more for facts, and self-reports for opinions, feelings, and experiences.
  8. Remember that counted data has limits too: it only includes what was recorded, such as crimes reported to police.

Common mistakes

  • Repeating a survey answer as if it were a measured fact.
  • Dismissing self-reports entirely. For opinions and experiences, asking people is the right method.
  • Assuming 'official' means counted. Many government statistics come from surveys.
You can do this when …, for three numbers in today's news, you can say whether each was self-reported or measured, and point to where it says so.

Sources

  1. Troiano et al. (2008), Physical activity in the United States measured by accelerometer (PubMed)
  2. CDC - About the National Health and Nutrition Examination Survey (NHANES)
  3. American Red Cross - 5 Skills to Save Your Life in the Water (example of a self-reported survey)

Sources and numbers last checked . How we check

Go deeper

ReportThe Basic Skills Report Card 2026We graded US adults on nine basics, most of which school rarely tests, from swimming to the fine print, with Canadian data where it exists. Six subjects got an F.GuideCan you swim well enough to save your life?Most adults say they can swim. Far fewer say they can do the five skills that get you out of deep water. Here is the standard, the data behind it, and how to test yourself safely.GuideHow to read terms, contracts and fine print in five minutesAlmost nobody reads the fine print, and nobody could read all of it. You do not need to. Five searches find the clauses most likely to cost you money.

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