A prediction is a statement or claim that a particular event will come to pass in the future. Prediction of future events is an ancient human wish. An apocryphal saying states: "it is difficult to make predictions, especially about the future". However, the desire to make predictions remains as strong as ever, and is an important part of almost every aspect of human life.

In a scientific context, a prediction is a rigorous (often quantitative) statement about what will happen under specific conditions, typically expressed in the form "If A is true, then B will also be true." The scientific method is built on testing predictions which are logical consequences of scientific theories. A theory whose predictions are not in accordance with observations will likely be rejected. In many scientific fields, desirable theories are those which predict a large number of events from relatively few underlying principles. Such predictions are the foundation of modern science and technology.

The place of prediction in the scientific method

In the scientific method,

• "'observe', 'wonder, react and guess', 'predict', 'test' and finally 'review'",
• a prediction is a logical consequence of some hypothetical explanation of an observation.

An example of prediction, by Semmelweis

In the 1840s the renowned Austro-Hungarian physician Ignaz Semmelweis noticed that women giving birth in the Vienna lying-in Hospital were dying in one building, but surviving in another.

His hypothetical explanation of this observation

He was forced to consider 'why?'.

• The difference was that the surviving women were attended by midwives and not by student physicians .

Thus the hypothesis:

• "the physicians were a factor in the deaths".

This horrifying proposition impelled Semmelweis to refine the factor.
What was the difference between the midwives and the doctors?

After more thought, Semmelweis decided that

• "the cadavers which the student doctors were touching must be part of the factor".

What could the doctors do to avoid the factor?

His predicted consequence, from the hypothesis

"If the doctors were to 'wash their hands', then the cadaver factor will be avoided"

A test of his prediction

Semmelweis instructed the student doctors to 'wash their hands', and the women who were attended by the doctors survived.

A review of the whole process

Semmelweis, 1861. The Etiology, Understanding, and Prophylaxis of Childbed Fever.

What did he know, and when did he know it?

In this prediction, Semmelweis did not know what the outcome would be. No one knew. In fact, the physicians were offended and outraged that their sacred profession could have been implicated.

Thus the element of surprise in a scientific result is essential, because the risk in the prediction is unavoidable. Before the process, Semmelweis did not know the answer. After the process, we all can know. This suggests that our sought-for certainty is a myth, at least in a scientific procedure.

Today, of course, hygiene in a hospital is routine, now that the phenomenon of infection is understood. But infection was not understood when Semmelweis made his pioneering investigation. Now we can afford the luxury of confidence in the work of Semmelweis, even if we cannot afford a myth of certainty.

Future topics

• past approaches to prediction
• the mechanistic universe
• the omniscience of God
• chance and probability
• modern scientific ideas
• is it possible to predict the future, even in principle?
  • quantum theory
  • limits on computability, and the holographic principle
  • chaos theory
  • phase space evolution
  • relativity theory and "block time"
• Prediction and forecasting in practice
  • Statistics
  • Simulation
  • Weather forecasting
  • Economic forecasting
  • Transport planning
  • Stock markets and Futures markets
  • Think tanks and futurology
  • Management of risk, for example, the Insurance industry
  • Extreme-value theory

Related topics

• failed predictions
• falsifiability
• fortune-telling
• free will and consciousness
• future of ...
• gambling
• hidden-variable theory
• hypothesis testing
• inference
• linear prediction
• logical induction
• oracles
• prediction interval
• probability theory
• prophecy
• psychohistory
• quantum indeterminacy
• randomness
• receiver operator characteristic
• retrodiction
• scientific method
• Seymour Geisser
• statistical prediction