Líkur

Líkur is the Icelandic term for probability or likelihood. It describes how likely it is that a particular event will occur and is used in statistics, risk assessment, and everyday judgment. In formal usage, líkur are expressed as numbers between 0 and 1, or as percentages, with 0 meaning impossible and 1 meaning certain.

In probability theory, a probability measure assigns a number to each event in a sample space in a way that satisfies certain rules: nonnegativity, normalization, and additivity. If A is an event, P(A) denotes its líkur. For two events, conditional líkur P(A|B) = P(A∩B)/P(B) expresses how the likelihood of A changes when B is known to occur. If A and B are independent, P(A|B) = P(A). Common models include the binomial distribution for the number of successes in fixed trials with probability p, and the normal distribution as an approximation for many natural quantities.

When people reason about líkur, two main interpretations are common: a frequentist view, where probability is the long-run frequency of outcomes, and a Bayesian view, where probability expresses a degree of belief updated by new information through Bayes’ theorem: P(A|B) ∝ P(B|A)P(A).

Applications of líkur appear across science, engineering, medicine, finance, and everyday decisions, such as predicting weather, assessing risk, or evaluating game outcomes. The concept provides a formal framework to quantify uncertainty and support rational decision-making under uncertainty.