I got to thinking the other day, which is always a very bad idea, but there you go, sometimes I just start and then can't stop. So, I picked a company that I have dealings with, and decided to work out how much they know about me.
My address - no big deal there of course, but they could then find out how much my house is worth, and probably how much I paid for it, and when.
My phone number - even if I didn't get it to them (and I probably did) it's going to be easy enough to get.
My age - fairly closely, though if I'm ever asked for my birth date I give it a year or so out.
My gender. Pretty easy, given my name.
Now, that's all basic stuff. Let's see what else they can work out.
If I'm dating someone, with (potentially) a rough indication as to their age
If I have any medical conditions
Drug related issues
How healthy I am
If I am an alcoholic
If I've got pets
If I live on my own, or have children
If I have children, how old they are
How often I have friends over
If I'm vegetarian or not
If I have any pets
If I have a car
If I prefer a shower or bath
How often I shower or bathe
What I like to read
What I like to watch on television, which channels and when
(Potentially) my sexual activity and sexual preference
My disposable income
If my parents are alive or not
How many children I know, or are close to, and their ages
Size of my house
If I have a garden, and how large it is
How susceptable I am to advertising
If I go on holiday, and probably where
How much I drive
Have you figured out which company I'm talking about here? If you'd said Facebook, you'd be wrong. Ditto if you said Amazon, but I can understand why you would have said either company. Similarly, it's not Google either. In fact, it's not primarily an internet company at all - it's Sainsburys. All of the things that I've mentioned above they could work out by watching by buying patterns via my loyalty card. Of course, the more that I shop in one chain, the more they'll know. I'm also guessing that I haven't actually even scratched the surface of what they could logically deduce from what I buy.
Suddenly, what Facebook/Google/et al know really rather palls into insignificance doesn't it! If you can think of anything else a supermarket could work out, based on your buying patterns, please add them into the comments - I'd love to see what I've missed out.