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'India may have got its tiger success story wrong'

February 24, 2015 09:33 IST
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A new study has indicated that methods commonly used in censuses of tigers and other rare wildlife put the accuracy of such surveys in doubt.

The study conducted at University of Oxford focused on the inherent shortcomings in the "index-calibration" method that means it can produce inaccurate results.

The team created a mathematical model to investigate index-calibration describing the approach and then tested its efficiency when different values, representing variations in data, were inputted. Under most conditions the model was shown to lose its efficiency and power to predict. The team then tested this mathematical model on a real world example: attempting to derive tiger numbers from fieldwork data. The index-calibration model was shown to be unreliable again, with any high degree of success shown to be down to chance, rather like being dealt a single incredibly 'high value' poker hand, that could not be replicated.

Arjun Gopalaswamy, lead author of the report from the Wildlife Conservation Research Unit at Oxford University's Department of Zoology, said their study shows that index-calibration models are so fragile that even a 10 percent uncertainty in detection rates severely compromises what they can reliably infer from them and their empirical test with data from Indian tiger survey efforts proved that such calibrations yield irreproducible and inaccurate results.

Dr Ullas Karanth, a co-author from the Wildlife Conservation Society, and a member of India's National Tiger Conservation Authority, said that this study exposes fundamental statistical weaknesses in the sampling, calibration and extrapolations that are at the core of methodology used by the government to estimate India's numbers, thus undermining their reliability and they are not at all disputing that tigers numbers have increased in many locations in India in last 8 years, but the method employed to measure this increase is not sufficiently robust or accurate to measure changes at regional and country wide levels.

According to the team the aim of the study was to help ecologists and conservationists to address the global challenge of counting rare and elusive animals.

The study is published in the journal Methods in Ecology and Evolution.

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