Why the sample of 200 startups from silicon valley is considered random?
Why the sample of 200 startups from silicon valley is considered random, when the sample of 50 students ( who are in nyu canteen) is not considered random? In the video it is mentioned that the sample of 50 students was not random because most of the students did not even get the chance to be in the sampling. Even, many other startups form USA(which are not in silicon valley) did not get the chance to be in the sampling, then how the sample of those 200 startups is considered random?
"You go to Silicon Valley and visit 200 start-ups in a random manner."
This sentence is meant to convey that you visit 200 random startups. The problem is that all of these random startups are located in Silicon Valley. So even though the sampling is random within Silicon Valley the sample is not representative of all startups in the USA (i.e. concentrated to one geographic location).
The same goes for the NYU Cantina students. You can ask random people in the cantina questions, but those students would not be representative of all students in NYU (i.e. concentrated to one area of the NYU campus).