Holistic example -
Question: What percent of people commute to college in Boston?
Where: BU, UMass Boston, BC
How: I will get a list of students from each school from all grades. I will then use a random number generator to pick 50 numbers between 1 and x (the class size) without repeats. For example, say the class size is 200 and the number generator picks 152, 103, 45... I will pick these numbers on the attendance list. After the 50 numbers are picked, those 50 people will be part of my sample.