On Monday, the IEA launched a substantial discussion paper making a set of practical proposals (“Plan A+”) to break the current deadlock in the talks between the UK and the EU.Consistent with our intellectual philosophy and educational purpose, it also made the case for shifting Brexit in a more free-market and outward-looking direction.As might be expected, the report had a mixed response, mostly favourable but also plenty that was unfavourable. This is, of course, fine by us. Our staff willingly engage with all sides, including at public events and across the media, despite the abuse (and worse) that often follows.The IEA is a small organisation run on a tight budget, mainly funded by individuals, trusts and foundations, without the resources of the civil service, government grants or big corporate lobby groups. We therefore especially welcome constructive debate and criticism, especially when this helps us to correct mistakes and improve our arguments.But Monday also saw one intervention that was very unhelpful, not just to us, but also to the general public. The BBC published an article by Christopher Cook, Policy Editor at Newsnight, headlined “IEA Brexit report based on dubious maths”.In my view, this crossed several lines. It is a misleading and personalised attack on the IEA and in particular on my colleague, Shanker Singham. It is also materially inaccurate.I am not making these complaints lightly. We have delayed responding to the article in order to give Mr Cook the opportunity to take our comments on board. However, we have not been able to agree. In the meantime, the original article is still being widely circulated and retweeted uncritically. We are therefore now publishing a detailed line-by-line rebuttal of the points made, here In summary, the article is fatally flawed for three, separate, reasons. First, Mr Cook attempts to discredit the entire IEA paper (of 149 pages) by focusing on just one number in one paragraph. This number is a preliminary estimate of the long-term gains in GDP that might be achieved across a group of countries from a reduction in anti-competitive market distortions.Despite the headline in the BBC article, no fair-minded observer could possibly conclude that the IEA report is ‘based on’ this one number, or the modelling behind it. Indeed, it forms part of a longer discussion of the difficulties of quantifying the economic impacts of Brexit. This whole section could be deleted without affecting the rest of the report.Second, the BBC article completely misrepresents the work that has been done in arriving at this estimate, and the processes behind it. The reader could be forgiven for thinking that the modelling is the sole work of Shanker. In fact, it is part of an ongoing collaborative project with external academic economists (just as the Plan A+ report itself was discussed with and reviewed by an external panel of trade specialists).Mr Cook is also simply incorrect to imply that the analysis is not based on conventional economic growth models or econometric techniques. He complains that we have not provided him with our complete model or dataset, which is true. But the work will be peer-reviewed for publication in an academic journal. In the meantime, it is unreasonable to expect us to respond to every request to share work that is still in progress.Third, Mr Cook’s attempts to replicate our results go completely awry and actually backfire. He states that he has not been able to replicate the results of the IEA modelling.This is wholly unsurprising, because he uses different methodologies and different data. Indeed, his own work is already unravelling.In the first version of the article he stated that his replication of the IEA model could only account for 40% of the difference in GDP between countries, compared to the figure of more than 90% that we have reported. But his own figure here has since had to be “updated” to 80%, following the intervention of someone presumably more familiar with econometric modelling.This huge change isn’t merely an “update” – it is a major correction, and one which actually reinforces the credibility of the IEA work. The fact that he was unable to replicate several other results, and comes up with bizarre ones of his own, again says more about his analysis than ours.To be clear, Mr Cook deserves credit for sharing his calculations and for his willingness to contribute to the debate, which we would not want to discourage. It is also good to see him acknowledge the positive role that independent think tanks can play.But attacks on the integrity and competence of IEA staff cannot go unchallenged. At the end of the day, it is his homework that needs to be done again, not ours.