I was thinking 5% was probably within the range of ordinary variations for a lot of domestically used chemicals .. that might mean one could already do such a study.

However, you have to get people to tell you how much product they use, which brands, how often, and not lie about it. That's basically impossible without antisocial levels of monitoring (which supermarkets probably already do, but which they don't want to tell their customers they do).

It's like the early days of mass customer data tracking where they'd tell customers they were probably pregnant, or probably gay, or whatever. People didn't receive the information in a way that suggested they were happy about the data being gathered.

It's probably too unethical to even use that data. Unless you're only trying to sell more crap, then it's A-OK! /s