Value of information (VOI or VoI) is the amount a decision maker would be willing to pay for information prior to making a decision. Similar terms VoI is sometimes distinguished into value of perfect information, also called value of clairvoyance (VoC), and value of imperfect information. They are closely related to the widely known expected value of perfect information (EVPI) and expected value of sample information (EVSI). Note that VoI is not necessarily equal to "value of decision situation with perfect information" - "value of current decision situation" as commonly understood. Definitions Simple A simple example best illustrates the concept: Consider the decision situation with one decision, for example deciding on a 'Vacation Activity'; and one uncertainty, for example what will the 'Weather Condition' be? But we will only know the 'Weather Condition' after we have decided and begun the 'Vacation Activity'. The Value of perfect information on Weather Condition captures the value of being able to know Weather Condition even before making the Vacation Activity decision. It is quantified as the highest price the decision-maker is willing to pay for being able to know Weather Condition before making the Vacation Activity decision. The Value of imperfect information on Weather Condition, however, captures the value of being able to know the outcome of another related uncertainty, e.g., Weather Forecast, instead of Weather Condition itself before making Vacation Activity decision. It is quantified as the highest price the decision-maker is willing to pay for being able to know Weather Forecast before making Vacation Activity decision. Note that it is essentially the value of perfect information on Weather Forecast. Formal The above definition illustrates that the value of imperfect information of any uncertainty can always be framed as the value of perfect information, i.e., VoC, of another uncertainty, hence only the term VoC will be used onwards. Standard Consider a general decision situation having n decisions (d1, d2, d3, ..., dn) and m uncertainties (u1, u2, u3, ..., um). Rationality assumption in standard individual decision-making philosophy states that what is made or known are not forgotten, i.e., the decision-maker has perfect recall. This assumption translates into the existence of a linear ordering of these decisions and uncertainties such that; di is made prior to making dj if and only if di comes before dj in the ordering di is made prior to knowing uj if and only if di comes before uj