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• A British man aged 55 has a check-up at the local clinic and is told that he has a small increased risk of having a heart attack within the next 10 years, compared to the average of all British men of his age. He is advised that treatment to lower his cholesterol level will reduce that risk.

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• A young child in India is in a road traffic accident and is admitted to hospital in an unconscious state. Her parents want to understand what the likelihood is that the child will recover in the next year, and what can be done to improve the chances of her recovery.

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• A pregnant woman in South Africa is found on a routine antenatal visit to have a raised blood pressure. Her doctor needs to calculate, and share with the mother, what the probability is, given available treatment, that the unborn child will be affected and how likely it is that the mother will have raised blood pressure 6 months after giving birth.

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These examples of interactions between people with health problems and their healthcare professional and healthcare systems concern prognosis.

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Prognosis in healthcare is the forecast of future outcomes in people with a particular health condition. For binary or time-to-event outcomes it can be can be expressed as a probability - “patients similar to you have a 90% chance of recovering from your back pain within one month” or “there is a one-in-five chance of perinatal death among infants born to women in South Africa diagnosed with pre-eclampsia during pregnancy”. (ref) For continuous outcomes, it can be expressed as an expected value - "for hypertension patients with your characteristics, we expect blood pressure at 6 months to be about 150mmHg".

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Doctors and other healthcare professionals use statements about prognosis to

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• inform individuals and their families about likely future outcomes and

• help make decisions with individuals and their families about the best care and treatments to improve those outcomes.

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Such evidence-based prognosis statements depend on robust findings from high-quality prognosis research studies.