Or something like that.
I'm fond of the quote "I'm too truthful to be good". But I also am fond of the remark about how folks who "love the brutal truth love the brutal part more than the truth part". So I've spent a lot of years working on trying to develop some desperately needed velvet gloves. If I can manage it (er, at least somewhat -- though this post might not exactly be a good example), surely you can. :-)
The "too truthful to be good" has a bit of danger in it; it seems to juxtapose goodness and truth, and I don't think they're mutually exclusive. I could just be misinterpreting it, though.
Peace.
A basic formulae could be a) acknowledge the positive attributes of the attempt (it is great to see you trying to optimize, and you are right to keep detailed numbers about what was going on, your funnel analysis was also spot-on.) b) Point out that he could do better. This emphasizes the growth potential instead of the shortcoming (one has an implicit expectation that the person can and will do better, the other is frequently taken as a rejection of the person.) An example might be: "you ran the test, but your test would be more helpful if you did it in a more controlled way..." c[optional]) suggest additional resources so the person can follow-up at their own pace, in the manner they prefer. Ex: (see this great post about having a control when testing your site...)
Now, if someone has ignored your previous feedback and it is your obligation to help them, things get a bit more nuanced.
This is exactly why I love this community.
In a face to face conversation, you can be nice all you want, because you have both time and non-verbal oppurtunities to make the point. The internet is different, for better and for worse.
Yes, the test had some serious flaws, but I imagine that removing the free plan was by far the biggest factor in the results - especially because there's no demo and no trial. I can't imagine signing up for a pay-only service if I can't even try out a demo of it before entering in my credit card.
I found value from the post, even though, yes, it is flawed.