We have three major modes of collecting the data. Each has its advantages and disadvantages. They are as follows:Personal interviews are the interviews conducted face to face. It has a high response and can provide open-ended questions. The reliability is high compared to other methods.Mailing questionnaires is sending a set of questions through emails. It doesn't disturb or consume the time of people. It also gives reliable answers without any inferiority or ambiguity. But we can't expect more people to answer.Telephone interviews are the interviews done by telephone. It is very cheap and provides more reliability. But consumes a lot of time and many people may refuse unknown calls.