When mildly castigating the Mumsnet survey on rape earlier this month, I missed a major blunder, which a reader has kindly pointed out.

My focus was on whether a self-selected online survey which is likely to attract only those with bad experiences means anything much. I compared the results Mumsnet reported with those of the British Crime Survey.

That was fine, as far as it went. But I overlooked the very strange way in which the survey was reported by Mumsnet. The PDF of the survey results on the Mumsnet website shows one question that read as follows:

Mumsnet reported this as 10 per cent reporting having been raped and 35 per cent sexually assaulted. But this ignores the third answer, those who have suffered both rape and sexual assault. Taking this into account, the true figure should be that 27 per cent have been raped and 52 per cent sexually assaulted, with only 38 per cent experiencing neither. Even worse than Mumsnet claimed!

The figures make it even more unlikely that the responses represent a true representation of women’s experiences, but the survey was widely reported, using the headline figures in the Mumsnet press release.

There was a second error in the press release, which stated that 23 per cent of respondents had been raped or assaulted more than four times. In fact, a full reading of the results page shows that the 23 per cent referred only to those who had earlier answered yes to rape and sexual assault questions, not to the whole sample.

My informant wrote to Mumsnet pointing out the errors. Mumsnet did not reply, but did correct the smaller error in the press release. The larger error remains uncorrected, and is still on the website, along with declarations of support for Mumsnet’s We Believe You campaign from David Cameron, Nick Clegg and Ed Miliband, among lesser lights.     

None, I suppose, read the small print or cared that this was a voodoo survey giving implausible results which were then wrongly reported. Such is the perceived power of Mumsnet that politicians fall over each other to back whatever it says, even when it’s nonsense. Oh, and the link to the PDF of the questions and answers has been removed, so it’s no longer possible to check the accuracy of the press release.

Never mind. My correspondent had already saved it, which enables me to attach it to this post.

I don’t trivialise rape. It’s a horrible crime. But carrying out dodgy surveys and then misrepresenting the results tends to trivialise the issue more than any unsympathatic man could do.