Population viability analysis (PVA) is an important tool in conservation biology. It is the process of predicting the risk of extinction from the combined effects of the deterministic threats — such as habitat loss, overexploitation, pollution and species introductions — and stochastic threats, including demographic, environmental and genetic fluctuations and catastrophes. This is typically done using stochastic computer simulations. PVA is also used to compare alternative management options designed to help threatened species recover. The technique arose in the 1980s but is based on the accumulated knowledge from more than a century of research in demography, ecology and genetics. In some ways it is similar to weather forecasting and the modelling of economics and global climate.