Question

Some polling agencies ask people to call a telephone number and give their response to a question.​ (a) list an advantage and a disadvantage of a survey conducted in this manner.​ (b) what sampling technique is used in such a​ survey?

Answer 1

Advantage: 
This usually results in a savings in the survey cost. As there is no need of travelling and meeting people in person. There is no need of much man power also.  
Disadvantage: 
There tends to be a lower response rate and this may introduce a bias into the sample. Only a certain segment of the population might respond. If you were in field there are chances of meeting random people from all segments of people. As the survey is taken through telephone ,the response of people who are not accessible to telephone can't be find.  
The technique used in this type of surveys are Convenience sampling.