Hello and welcome to More or Less, your guide to the numbers in the news and all around us in life here on the BBC World Service.

This week is Insect a Gaden heading our way.

We're going to be looking at a global scientific review on the population of bugs which came out in February.

The results were shocking. It said the mass of insects is falling by 2.5% a year,

41% of insects are threatened with extinction and if that doesn't sound bad enough, there could be no insects left on Earth in a hundred years according to the first global scientific review.

But the world is truly under threat, scientists say, from a catastrophic collapse of nature's ecosystems.

But some more or less listeners questioned the findings.

Wide spread reports of insects in decline by 2.5% per annum.

How can anyone estimate this? Has someone counted them all? If so, how? Is this true?

All insects have become extinct in a hundred years. Seems to me to be too fantastical to be remotely likely.

So are our listeners onto something? Well let's start at the beginning.

This new piece of research is a matter analysis by two authors from Cisco Sanchez Bayo and Chris Vake Hayes.

They didn't count any insects themselves, but instead analyse lots of studies by people who have gone out and counted insects.

So the first important question is how did they choose which studies to include?

Well they did a search of a database of scientific papers and they put in the terms insect survey and decline.

And that threw up more than 600 surveys and they then focused in on 73 of those papers.

Caspa Albers, a statistician from the University of Groningen in the Netherlands, questions their methods.

So what they did is they only looked for papers that had the keyword decline in the title or abstract.

It could be that there are also papers that actually found an increase, but if you look for this keyword, you won't find those papers.

So they kind of introduced a bias in the way they looked for their papers.

Now we've had Professor Kevin McConeway of the Open University in the UK run a search for us in the same database, but using increase as a search term rather than decline.

And that produced more than three times as many academic studies are searching for decline.

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