After I purchased my home in 1994 I learned that my house is one that the U.S. Census Bureau visits every two years. So, since 1994, all that interesting statistical data the Census Bureau compiles during the years between the complete censuses likely includes information gleaned from me.
And now I've become a source of data for another large survey. The University of Michigan produces a Health and Retirement Study of people age 50 and older that they update every two to three years. Last year I was invited to participate, apparently met the qualifications, and this evening sat through my first survey interview. Unlike the Census Bureau, which targets a specific residence, the U. of M. study follows the individual. So, for the rest of my life, they will be tracking me down wherever I go.
Unlike the U.S. Census Bureau, which I'm expected to participate in as a good citizen, the U. of M. pays for my time. And they pay pretty good, all things considered.