You may have counted a higher or lower proportion of a species than is truly the case. Conclusions may be problematic. Suppose three classmates say they never eat chocolate. Alternatively, suppose that all three confess to eating buckets of chocolate. Environmental scientists usually conclude that if no impact is detected, none exists.
Models are important tools for environmental scientists.
Atmospheric scientists design models, predict possible outcomes and develop policies like the Kyoto Protocol. It is not acceptable to log the forest, then find that the owl cannot, or does not, survive. PVA is a useful, non-invasive way of establishing the basis for proper management. The precautionary principle is used to justify action to stop a suspect cause pending further study. Neil Champion is the science manager at the Victorian Curriculum and Assessment Authority.