 Regimented decision-theoretical usage differs from this. In decision theory, a decision is said to be made “under risk” if the relevant probabilities are available and “under uncertainty” if they are unavailable or only partially available. Partially determined probabilities are sometimes expressed with probability intervals, e.g., “the probability of rain tomorrow is between 0.1 and 0.4”. (The term “decision under ignorance” is sometimes used about the case when no probabilistic information at all is available.) 