Health literacy
Writing for the reader who can read the words but cannot use the numbers. For most health content, that is most readers.
The rule
Write for a reader who understands every word and still cannot answer the question. Health literacy is not the same as literacy. It is the ability to find, understand and act on health information, and its numerical part is health numeracy, which fails far more often than the vocabulary part.
That reframes the job. Replacing "hypertension" with "high blood pressure" is necessary and it is the easy half. The hard half is that a reader who fully understands "your reading is 148 over 92, and the usual range is 90 to 120 over 60 to 80" may still not be able to answer should I do something about it? That is the only question they opened the app to ask.
Four rules follow.
- Answer the question the reader has, before the one you have data for. They asked "am I OK?". You have a number. The sentence must bridge the two, and the bridge is the comparison and the action, not the number.
- Never make the reader do arithmetic. No mental subtraction, no percentage of a percentage, no unit conversion, no reading a value off an axis. If a comparison matters, write the comparison.
- Give the frame with the figure. A number with no reference point is not information. "72" is nothing; "72 bpm, which is within your usual range of 58 to 76" is an answer.
- Assume interruption. Health content is read while distracted, while frightened, on a bus, in a corridor, one-handed. Every paragraph must survive being the only paragraph the reader gets to.
Writing about risk
Risk is where numeracy fails hardest, and it has its own canonical page: Risk and statistics owns the rules and the evidence. The content-side summary is short:
- Absolute, never relative alone. "Increases your risk by 50%" is uninterpretable and usually alarming out of proportion to the underlying change. Give the two absolute figures.
- Natural frequencies, one denominator. "About 3 in every 100 people" beats "3%", and both denominators in a comparison must be the same number.
- Never a bare percentage in a sentence a reader is meant to act on.
- Say what the number does not cover. A risk figure derived from a population is not a statement about the person reading it, and the sentence must say so.
Approved / Rejected
Do
Don’t
The rejected version is accurate, precise, and asks the reader to compute their own answer from a percentage of a statistic they have never seen.
Do
Don’t
The figures in that pair are invented to show the shape of the sentence and carry no clinical meaning. Real frequencies come from whoever owns the clinical content in your product; a design system must never supply them.
Do
Don’t
Patterns
The three-part answer. Almost every health value sentence is the same shape:
What it was.How that compares.What to do, or that nothing is needed.
Filled: "Your reading was 118 over 76. That is in your usual range. Nothing to do. Your next check is on Friday."
The comparison, written out
That is
higher / lowerthanyour usual range,your average for the last 30 daysoryour reading on a named date.
Never "above baseline", "outside parameters", "deviating from your norm".
The frequency
About
nin every100peopleoutcome. That means about100 − nin every 100 do not.
The unknown
We do not have enough readings yet to say whether this is a trend.
nmore readings and we will be able to show one.
The clinical term, introduced once
Plain phrase. Your GP might call thisclinical term.
Not the other way round. The reader's word leads; the clinical word is the footnote, because the reader needs to recognise it on a letter, not to use it.
Layout is part of literacy
Three formatting decisions carry more comprehension weight than most word choices: the answer is in the first line and not behind a tap; the number and its comparison are adjacent, not in separate cards; and the action is a control, not a sentence a reader has to convert into a plan.
Banned words
| Banned | Why | Use instead |
|---|---|---|
| baseline, parameters, norm | Clinical register for a comparison the reader owns. | your usual range, your average |
| adherence, compliance | Describes the reader as an instruction being followed. | how often you have logged |
| percentile, standard deviation, confidence interval | Not usable by most readers, and rarely necessary. | a natural frequency, or nothing |
| a bare % in an actionable sentence | Percentages of unstated denominators are the classic numeracy trap. | n in every 100 |
| mean, median | Statistical register. | average, middle value |
| trending upward, on an upward trajectory | Implies a trend that two points cannot support. | higher than last time, and say how many readings you have |
| optimal, ideal, target (unassigned) | Implies a goal nobody set with the reader. | the range your GP gave you, or delete |
Related components
Valueis the number and its unit; the frame that makes it interpretable is the caller's responsibility and this page is what that responsibility means.RangeBaris the comparison made visual. It must still ship the comparison in words, because a picture of a comparison is not a comparison for everyone.ResultCardtakes the three-part answer above as its content contract.Termintroduces a clinical word once, in the reader's own sentence.TrendSparklinemust not be shown before there are enough readings for a trend to mean anything; the "not enough yet" sentence is on this page for a reason.
Voice and tone
One voice, four tones. The voice is calm, plain and in the second person, and the register is set by the seriousness of the news rather than by the brand.
Plain-English A to Z
The canonical clinical-to-plain vocabulary, the rule for choosing a replacement word, and the machine-readable list every product and Term instance shares.