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Ronny Kohavi: prediction

27 Jul 2023 Lenny's Podcast The ultimate guide to A/B testing | Ronny Kohavi (Airbnb, Microsoft, Amazon)

“Hold that dinner, investigate, see, because there's a large probability that something is wrong with the result. And I will say that nine out of 10, when we call it Twyman's law, it is the case that we find some flaw in the experiment.”

— Ronny Kohavi

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Everything needed to verify it.

Speaker
Ronny Kohavi
Attribution
Verified speaker
Claim type
prediction
Recorded
27 Jul 2023
Publisher
Lenny's Podcast

Transcript context

…Which is a great segue to something you mentioned briefly, something called Twyman's law. Yeah. Can you talk about that? Yeah. So Twyman's law, the general statement is if any figure that looks interesting or different is usually wrong. It was first said by this person in the UK who worked in radio media, but I'm a big fan of it. And my main claim to people is if the result looks too good to be true, your normal movement of an experiment is under 1% and you suddenly have a 10% movement, hold the celebratory dinner. It was just your first reaction, right? Let's take everybody to a fancy dinner, because we just improved revenue by millions of dollars. Hold that dinner, investigate, see, because there's a large probability that something is wrong with the result. And I will say that nine out of 10, when we call it Twyman's law, it is the case that we find some flaw in the experiment. Now there are obviously outliers. That first experiment that I shared where we promoted that made long titles, that was successful. But that was replicated multiple times, and double and triple checked, and everything was good about it. Many other results that were so big turn out to be false. So I'm a big fan of Twyman's law. There's a deck, I could also give this in the note, where I shared some real examples of Twyman's law. Amazing. I want to talk about rolling this out of companies and things that you run into that fail. But before I get to that, I'd love for you to explain P value. I know that people kind of misunderstand it, and this might be a good time to just help people understand, what is it actually telling you, P value of say 0.05?…

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