An important thing you’re missing is the control. You should record every ad.
You need to know if you got 3 topics of ads every day and 1/3 of them are related to that secret topic, OR if you get 300 topics every day and 1/300 are related to that secret topic. If it’s the former, it’s suspicious, if it’s the latter, it’s way less suspicious.
The control is the topic you pick that you don’t discuss on WhatsApp or messenger. The idea is random differences between topics should average out over many trials.
I still think it’s important to consider the volume of topics that show up that aren’t being explicitly looked for.
I’ve gotten Instagram ads for ketamine and I absolutely am not discussing or searching for it. I probably wouldn’t even notice a random topic if it’s not so absurd. I’m sure there’s tons of topics I don’t even realize I see.
The reason for the control I suggested is to try to counteract the bias people have towards noticing things they recently thought about. I think the question of what adverts people are shown in general is interesting but quite separate.
You need to know if you got 3 topics of ads every day and 1/3 of them are related to that secret topic, OR if you get 300 topics every day and 1/300 are related to that secret topic. If it’s the former, it’s suspicious, if it’s the latter, it’s way less suspicious.