If you’re not crowding into a store today, it might be because personalized sales offers are coming to you. Those offers might be based on what you usually spend, whether or not you take a yearly vacation, how many kids you have and even what kind of laundry detergent you usually buy.

Matt Carmichael is a journalist who studies data, and wrote the book “BUYographics: How Demographics and Economic Changes Will Reinvent The Way Marketers Reach Consumers.” He followed a small group of families around to how they were spending their money and what money choices they were making.

Carmichael says the middle class is shrinking in some ways and evolving in other ways and that has led to all sorts of interesting tradeoffs. “In terms of how we spend money, what have typically been competitive spaces aren’t what we think they are anymore,” Carmichael says.

In the book, he uses a person named Liz as an example. Liz was trying to save up to buy a laptop and she couldn’t reach her saving goals because her friends kept getting married and she spent the money on attending their weddings. “The laptop maker isn’t necessarily looking at the bridal industry as a competitor, but because of the changes in our income and because of the changes in our middle class you start seeing product categories competing in ways that they haven’t before,” Carmicheal says.

And that research Carmichael provided was valuable to the families he studied, too.

Carmicheal says one of the most interesting cases was a woman from East Baton Rouge Parish, Louisisana named Sandra. Sandra is a single mother of two girls and she’s burdened with all the things that a lower class single parents are burdened with. “As we were talking, she started to realize that she wasn’t really taking care of herself very well, and she started to think you know maybe I actually treat myself a just little bit better and we’d all be better off,” he says.