How many times have you wanted to try something new, but was not sure it is was going to be exactly what you hope it to be, so you look at customer reviews online to see what others say about it?
I do that too. EVERY TIME.
Above are links to three very popular review sites. Rottentomatoes gives reviews on movies, zagat gives reviews on restaurants, and ratemyprofessors give reviews on teachers.
Each review that a customer posts on a product or event on a website is a method of research. The website host is the surveyor and is collecting information via a convenience sample. Every review that is written comes from a participant who voluntarily chooses to share their opinions. But the public use these reviews as a type of opinion leader and most of the time allow the review to persuade them to how they perceive the product. Thus reviews have a lot of power.
If you are unsure is the new restaurant in town is any good, if you see a review where other users have ranked it at a 97%, you are not going to have any hesitation about going to eat there that night. But if the review is only at 28%, that restaurant will probably be going out of business soon.