Need some explanation on Question 2
Can you tell me why visiting 200 start-ups in a random manner cannot be considered representative? does picking the random 200 startups from random silicon valley violated the representativeness of sample data?
Because the population of interest is USA, so the 200 start-ups should be randomly selected from the whole USA (i.e. the sampling procedure should include all start-ups in the USA, instead of only from Silicon Valley).
If the researcher is interested in the study of start-ups in the Silicon Valley only, then a sample of 200 start-ups would be represenative.
Hope this helps.