Uncertainty in statistics is measured by the amount of error in an estimate of the mean or average value of a population. The sample mean is the average of a group of measurements or parameters taken from the population, and the standard deviation of the mean provides an estimate of the uncertainty that any one measurement will represent the true mean of the population. In environmental science, it is often very difficult to make enough measurements of interacting processes so that uncertainty in the estimate of the mean values of important parameters is low enough to prove whether hypotheses are correct or not. Baysian statistical analysis is a statistical method that estimates the probability that a hypothesis is true, then modifies and updates the probability as more studies are conducted and more information becomes available.