[srean]

I used to be skeptical about this and would try and find alternative explanations, for example, cognitive biases, coincidences, search requests from another device routed through a common wifi.

However, I have changed my mind through a lengthy process of attrition of possible explanations.

Recently my wife was around her friend who was having a vertigo spell. We talked about it when we met. None of us searched about it. Lo and behold my YouTube feed has videos on how to mitigate vertigo.

It's possible that they transferred information across two phone devices that came in close proximity, the owner of one who has a history of vertigo. But even that is a stretch, why transfer 'vertigo' specifically ?

[gambiting]

>>Recently my wife was around her friend who was having a vertigo spell. We talked about it when we met. None of us searched about it. Lo and behold my YouTube feed has videos on how to mitigate vertigo.

Again, while the simplest explanation is the most tempting one, we just have to consider that Google has an absolutely stunning amount of information on any of us. Like, it definitely knows your friend is your friend. It knows what your friend searched for recently, and it knows you met and spent some time together. So of course it makes sense to show you videos about some stuff that it marked as "interesting" for them. They are probably getting videos for stuff that you have looked up recently, whether you talked about it or not.

[srean]

Yes, as you would note, this was one of my hypotheses. However, it is on shaky ground.

This friend has suffered from vertigo chronically, it was not a new one off. My wife's and her friend's phones have been close proximity many many times before. It's certainly odd that Google would recommend vertigo only after a vertigo spell happened in the presence of my wife. None of the three searched for vertigo.

Phone motion sensors detecting a vertigo spell ? Well that's a possibility, but I doubt Google would be running such a detector 24x7, seems too expensive, unless the opportunity to show a timely ad is lucrative enough to cover the cost.

Although none of the three searched for vertigo, the friend may have searched for her pharmacy to refill her meds.

This is not the only incident. I have come to believe what I now believe about this eavesdropping, after a long period of whittling out competing hypotheses. I would usually file these incidents under confirmation bias. But these have happened just too many times.

A quantative Bayesian analysis would have been the right thing to do. On that count I am delinquent. I will, however, grant you this, human intuition is terrible at Bayesian analysis and tends to see significant patterns when there are none.

[program_whiz]

The reason occam's razor works is useful is it draws the one line connecting two points, rather than any squiggle that passes through them.