Conservation and management of biodiversity require measurement of biodiversity because it is important to make choices about "what, where, and how" to conserve. Measurement can be considered at all three levels of biodiversity: genes, species and ecosystems. As they are all interrelated, however, it is difficult to talk about measures at one level while ignoring the others. It is also difficult to measure biological diversity because there are so many ways of measuring it, and the situation is made more complex because of problems associated with the interpretation of data resulting from the different forms of measurement.