This week Nora Hansen, member of the Working Group on Marine Mammal Ecology (WGMME) defines what is meant by statistical power.
'As marine mammal scientists, we are often interested in measuring the changes in numbers of animals that are counted during surveys. Often, the magnitude of change in population size is used as an indicator of how well or poorly a population is doing. So it is important that we are clear about our confidence in the size of the change.
Statistical power is a measure of our confidence in the presence and size of an effect we observe. It is usually expressed as a percentage and refers to the chance of not making a false negative error. In this context, a false negative would be concluding that there has been no significant change in animal numbers when in fact there had been.
So if statistical power is 90%, for example, it means we can be 90% confident that we detect a change in population size when there really is one.'