# Fact box 3.5 Uncertainty in the resource estimate

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Uncertainty expresses the range of possible outcomes or results. This can be described in many ways, most often with the aid of high or low estimates.
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The NPD estimates, for example, that 2 200-6 200 million scm oe remain to be identified on the NCS. Uncertainty is calculated using Monte Carlo simulations (a statistical method), with high and low uncertainties described using statistical concepts. Where undiscovered resources are concerned, the NPD generally uses P_{95} for the low estimate.

This means that, given the assumptions applied in the analysis, the probability of a result equal to or larger than the P_{95} value is 95 per cent. P_{05} is used for the high estimate, which means a five per cent probability that the result will be equal to or larger than the P_{05} value.

The expectation value is the average value. This is generally defined as the arithmetic mean of all the outcomes in the statistical distribution. It is much used, and has the property that the expectation value for various distributions is the sum of the expectations.