Ask HN: I bought Voltaren at the chemist, now Google shows me ads for it. Why?

And even if you pay via card/phone ( which is literally multiple times faster and less hassle), the payment processor and card issuer don't know the individual items.

Here are two (abridged) definitions from the Oxford dictionary:

1. conforming to the law or to rules

2. make legitimate; justify or make lawful.

You're choosing to ignore the verb make in the second definition, describing the act of conferring legitimacy on something, which necessarily implies that it was previously lacking.

One of the three deviated and searched for nappies online prior to the trip.

Rather than relying on external people to make judgement, you could test the hypothesis yourself: write on paper a phrase. Spend one week without ads and document all ads you see. Spend second week saying word N times per day. Also document all ads you see.

Ask N people to do this and report your findings, then you might provide statistical insight and validate your hypothesis.

Otherwise, who's to say one of those students didn't Google it before the trip?

Does anyone have any ways to improve the design of the above experiment?

Its common and help companies target clients with ads on the internet in general (YouTube, sites, etc).

It works like that:

- The Chemist wants to sell things online or physically.

- They pay google for ads for their products on sites related to its business lines or keywords about its niche.

Google then show their ads for people in general, people interested on those subjects or to people visiting sites about those subjects.

Interest is determined by search history and navigation (every google ad in a site (chemist or not) help google know you were there).

Then the chemist want to target past customers with more specific ads (like reminding people of items in theirs carts):

- They send google ads information about clients and past physical or online purchases / interactions.

Google then match the user with its own database and connect the sent data with its own data.

- Now the Chemist benefits from the google (because google can find you online)

- Now other google clients benefit from this data (because now your google hidden profile is more accurate about your interests and habits)

- Now Google benefits from that because it can use the purchase data to hone its models about ad-to-spend.

The chemist also want to pay google a fraction of the purchases if the client saw an ad.

- Google uses information sent in realtime by the Chemist and other companies, model this data and determine which people, sites and subjects have a bigger probability to turn an Ad into a sell.

I have myself done that in the past and Facebook was quite accurate at turning ads into course subscriptions.

Better to focus on privacy laws.