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#BadScience: Oxford researchers find India’s Tiger numbers were based on unreliable methodology

It was an issue that evoked celebrations from no less a figure than Amitabh Bachchan.

Research which suggested that India’s Tiger population had grown by a massive 30 percent in a four-year period ending 2014, the legendary Bollywood actor said, was the “greatest joy”.

Mr Bachchan had joined India’s Save The Tiger campaign in 2010 and took to his blog in late 2014 to announce that the number of tigers had risen from 1411 in 2010 to 2226.

Those figures however, have been called into question by scientists at the University of Oxford as well as the Indian Statistical Institute and the Wildlife Conservation Society, who claim that the statistics were based on a flawed methodology.

That methodology is one which has previously been used by scientists around the world but one that has now been deemed “unreliable”.

The so-called ‘Index calibration’ method relies on measuring animal numbers in a relatively small region using data taken from reliable and high-tech sources such as cameras.  These numbers are then compared and calibrated with data taken from less reliable, and distinctly low-tech methods, such as paw prints.

That data is then used to estimate the number of animals in a larger area. 

However, researchers at the Department of Zoology at the University of Oxford created a mathematical model to test the reliability of the model which revealed that obtaining accurate and reliable data was akin to being dealt a single high value hand at a poker game.

Arjun Gopalaswamy, of the Wildlife Conservation Research Unit at Oxford University’s Department of Zoology and one of the scientists who tested the methodology, said: “Our study shows that index-calibration models are so fragile that even a 10% 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”.

Dr Ullas Karanth, a member of India’s National Tiger Conservation Authority, said: “This research 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. We are not at all disputing that tigers numbers have increased in many locations in India in last eight years, but the method employed to measure this increase is not sufficiently robust or accurate to measure changes at regional and country wide levels”.

The University’s findings will be published this week in the journal Methods in Ecology and Evolution.

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