What kind of people were questioned in the man’s survey?

W: Your survey sounds very good. How many people filled it in?
M: I gave out 120 copies and got 70 back.
W: That’s a very high rate of return. Who did you give your questionnaires to?
M: I gave a copy to every student in my residence hall and a few to my friends from other colleges.
W: Don’t you think this might influence your survey results?
M: What do you mean?
W: Students in your hall of residence might be of the same age. This means that they might have similar opinions. In this way, your results represent only student opinion, not public opinion.
M: So how are you going to do your research?
W: I’m going to interview my respondents in the shopping mall. If they agree, I will ask them some multiple-choice questions and note down their answers on my sheet. I will select people of different ages and attitudes, so that my sample people would be reasonably representative.
M: Isn’t it very difficult to ask meaningful questions using multiple choices?
W: Yes, it is. I suppose your survey has the advantage of more detailed information. The secret to writing a successful survey is to write simple questions that target at the information you are looking for. Therefore, it is better to write a lot of short specific questions than longer general ones.
M: So that’s why it is taking you so long to write your survey.
W: Yeah, but I hope I will be ready to start interviewing this coming weekend.