Rethink Using 'Rare' to Describe Risk
By Dr. Lynora Saxinger
Communicating Medical Numbers
Have you ever told a patient a side effect is “rare”, “unlikely” or “common”? To you, “rare” might mean <1%. To your patient? It could mean anything from 0.01% (1 in 10,000) to 10% or more.
A recent JAMA article breaks down how we should communicate medical numbers. It highlights a massive gap between how clinicians think they’re communicating risk and how patients actually hear it. Using imprecise terms can accidentally mislead. Patients can have varied numeracy skills. We don’t want to accidentally nudge patients into decisions they might not otherwise make. The following is a classic example.
The "half-off" trap
If you tell a patient, a drug "cuts their risk of a stroke in half," they’re usually all-in. But if that means their risk drops from 2% to 1%, that 50% relative reduction feels a lot less heroic when framed as a 1% absolute benefit. By omitting the baseline, we create an "illusion of certainty" that can lead to over-treatment and misaligned expectations.
The Precision Prescription:
Why Your Risk Communication Might Be a Problem, and How to Fix It
Let’s be honest: most of us went into medicine to help people, not to be math teachers.
But the truth is, every time you discuss a treatment plan or a prognosis, you are teaching math.
A recent JAMA viewpoint, by experts Brian Zikmund-Fisher, Alicia Thorpe, and Angela Fagerlin, points out that HOW we present numbers can dictate patient choices more than the actual facts do. If we aren't careful, we aren't informing patients, we’re accidentally manipulating them.
Here is the evidence-based toolkit to ensure your patients actually hear what you’re trying to say.
1. Kill the Lone Adjectives: The "Rare" Problem
We love words like "unlikely," "common," or "infrequent". They feel conversational and understandable. The problem? They are mathematically meaningless.
Studies show that when a clinician says a side effect is “rare,” one patient might think that means 1 in 10,000, while another thinks it means 1 in 5.
If you tell a patient a complication is "low risk," they might interpret that as essentially 0%...and then feel betrayed when it happens to them.
The Fix:
Always anchor your adjectives with a hard number.
- Don't just say "It's rare."
- Say, "It’s rare—it happens to about 1 in every 1,000 people."
2. The Marketing Trap: Relative vs. Absolute Risk
If you want to sell a drug, you talk about relative risk.
If you want to practice ethical medicine, you talk about absolute risk.
Imagine a new treatment that reduces the risk of a major cardiac event by 50%. A lot of people would jump at the chance.
But, if the patient’s baseline risk is only 2%, that "50% reduction" brings them down to 1%. Thus, factors like affordability and side effects start to be more important, as the absolute benefit is a measly 1%.
When we only give the relative number (50%), we create an "illusion of certainty." Patients overestimate the benefit and are more likely to consent to treatments that offer very little marginal gain.
The Fix:
Provide the "before and after" to help them understand how likely something is to help them or hurt them.- “Out of 100 people like you not taking this drug, 2 will have a heart attack. If all 100 take the drug, only 1 will have a heart attack.”
3. Stop the Denominator Dance
Our brains are surprisingly prone to ratio bias.
If you tell a patient, they have a "1 in 10" risk of a reaction, and then say another drug has a "5 in 100" risk, many patients will focus on the "5" and think the second drug is more dangerous—even though the risk is actually half as much (5% vs 10%).
Instead, compare Drug A and Drug B as “10 of 100 versus 5 out of 100 people.”
Another example: in an effort to increase precision, we may use comparisons such as “1 in 112 versus 1 in 384.” This precision can add complexity, and many people may misinterpret what it means.
The Fix:
- Keep your denominators consistent. Pick a base (usually 100 or 1,000) and stick to it for the entire conversation.
- Prefer phrases like “8% of people” and “about 3 in 1000 people.“
4. Framing: Survival vs. Mortality
The way you "frame" a number can trigger a purely emotional response that bypasses the patient’s logic.
If you tell a patient that a surgery has a "90% survival rate", they will likely feel hope. If you tell them it has a "10% mortality rate," then they will likely feel fear.
Research shows that patients (and even experienced physicians!) make different clinical choices based on which frame is used, even though the math is identical.
The Fix:
- State both sides or use "double framing." Present both the positive and the negative can neutralize the emotional bias.
“This means that out of 100 people, 90 will come through the surgery and 10 will not.”
5. Visuals as Tools for Clarity, Not Simplification
We may avoid visual aids because they don't want to seem patronizing. But for patients with lower numeracy (which is a large portion of the population), talking about numbers may just sound like noise.
Icon arrays (those grids of 100 little stick figures where a few are colored) and stack bars (“part to whole” displays) are the gold standard. They help patients visualize on the "denominator" or the 99 people who didn't have the side effect, instead of hyper-focusing on the one person who did.
The Fix:
- Draw the array/dots (graph paper can help), or create a visual with an app (here's a useful free icon array generator).
- Taking 30 seconds to provide a visual, can save 30 minutes of confusion later.
6. The "So What?" Factor
Finally, numbers aren't the goal...meaning is. For example,
- A 5% risk of a tremor might be "low" to a cardiologist, but can be catastrophic to a professional violinist.
- Saying their platelet count is 75, and normal is 150 to 400, is partially helpful. Adding that “we would cancel the procedure if it is below 50” provides context.
Consider, with the patient, "What does this number mean for your daily life?"
The Bottom Line
Communication is a clinical procedure. Just as you wouldn't use a muddy scalpel, we shouldn't use muddy numbers.
Switching to clear, consistent, absolute numbers and double framing allows us to move from being a source of possible confusion to a source of guidance.
Precision medicine requires precision talk. Let's make it count.
Reference:
Zikmund-Fisher BJ, Thorpe A, Fagerlin A. How to Communicate Medical Numbers. JAMA. 2025;334(16):1474–1475. doi:10.1001/jama.2025.13655
Dr. Lynora Saxinger
Director, Scientific Communication
Professor, Division of Infectious Diseases
Department of Medicine, Faculty of Medicine & Dentistry