The psychology of searching for hard-to-find species

Base-rate neglect, inverse-probability fallacy and poor environmental decisions

Our big brains struggle to coherently combine probabilities. It’s something that’s been noted time and again in studies on how doctors interpret a medical diagnosis but it’s a basic problem whenever we are presented information with several points of uncertainty (consider the blue cab / green cab problem on the right). And this is a big problem commonly encountered in environmental management whenever we have imperfect detection.

When can we declare successful eradication of a weed? Or when do we accept a species has gone extinct? What’s the chance a contagious disease is still present in an animal population, despite negative tests on a subset of individuals? If we allow development at a site, what’s the chance an endangered species is present even though it hasn’t been found in biological survey records? In acquiring land for conservation reserves, how confident are we that species of interest are actually captured by the reserve network? The first four problems allude to the costs of false absences (and all have been discussed in past issues of Decision Point, see the box on ‘missing the point’). The last is more about the cost of false presence. In all cases, Bayes Theorem can be used, so long as we have pre-diagnosis estimates of prevalence (from a model, or sparse data, or expert opinion) and we’re able to hazard a guess at the reliability of our diagnostic ‘test’ (mammogram, blood test, biological survey)…





Leave a Reply