Web intercept (also known as river) samples
“网络拦截式（亦称钓鱼式）抽样调查”

‘River sample, or web intercept sample, involves placing banners,
ads, or promotions on a variety of websites so that people will click on
them and subsequently complete a research survey.

It is called River Sampling because it is similar to fishing in a river.
When your fishing line hits the water, you don’t know the color or size or
variety of fish you might catch and you don’t know anything about
where the fish has been or what it has done. Once a fish is caught, it is
pulled out, (surveyed), and then placed back in the river. The chances
of catching it again are very unlikely.’

http://web.peanutlabs.com/wp-content/uploads/2014/08/PL-Rive...