[ploxiln]

If I recall the youtube slow-internet optimisation case correction, I think it is an example of Simpson's paradox. They made it faster for countries with fast internet, and faster for countries with slow internet, and then the average performance across all users/countries was slower, because now the countries with slow internet used youtube much more than before.

[lordgrenville]

But the improvement induced the demand, which to my mind makes this different from Simpson's Paradox.

[bryanrasmussen]

I would say the improvement allowed the demand to be met, everybody wanted to use youtube, but few could.

Just like many people may want to eat a wide range of expensive tasty food, but have to make do with junk because it's what they can afford.

[mFixman]

It would be Simpsons' Paradox if Google services in Indonesia were initially slow because Indonesians tend to use YouTube more often than lighter services.

There wasn't an error in the conclusions of the initial measuremen. It was the solution that had problems.

[lern_too_spel]

Doesn't matter. That is not relevant to the paradox.

[kgwgk]

How does "Average and p95 latency actually increased after shipping the work to production. How does an objectively good change make things worse?" relate to Simpson's paradox again?

[ploxiln]

That's exactly it. After "shipping the work to production" (making it faster for everybody), the overall average and p95 got worse. Each sub-population experienced improvement: countries with fast internet got faster youtube, countries with slow internet got faster youtube. But the overall average and p95 got worse: overall average was slower youtube. Because now more users from the second sub-population bring the overall average speed down (or latency up). That's Simpson's paradox.

[kgwgk]

Ah, you may be right. It's not clear in the story that "Average and p95 latency actually increased after shipping the work to production." means average of Indonesia and ex-Indonesia and not just Indonesian average.