A team of scientists from the University of Oxford, Indian Statistical Institute, and Wildlife Conservation Society exposes, for the first time, inherent shortcomings in the 'index-calibration' method that means it can produce inaccurate results. Amongst recent studies thought to be based on this method is India's national tiger survey (January 2015) which claimed a surprising but welcome 30 percent rise in tiger numbers in just four years.
The team urges conservation practitioners to guard against these sources of error, which could mislead even the best conservation efforts, and suggests a constructive way forward using alternative methods of counting rare animals that avoid the pitfalls of the index-calibration approach.
A report of the research is published this week in the journal Methods in Ecology and Evolution.
Arjun Gopalaswamy, lead author of the report from the Wildlife Conservation Research Unit at Oxford University's Department of Zoology, said: 'Our study shows that index-calibration models are so fragile that even a ten per cent uncertainty in detection rates severely compromises what we can reliably infer from them. Our empirical test with data from Indian tiger survey efforts proved that such calibrations yield irreproducible and inaccurate results.'
Arjun added: 'Index-calibration relies on the assumption that detection rates of animal evidence are high and unvarying. In reality this is nearly impossible to achieve. Instead, there are many flexible approaches, developed over the past decade by statistical ecologists, which can cut through noisy 'real world' data to make accurate predictions.'
Image courtesy of Shutterstock/ehtesham