Answer to Question 1
A traditional mail survey is a self-administered questionnaire sent to respondents through a postal service. This paper-and-pencil method has several advantages and disadvantages. Mail questionnaires can reach a geographically dispersed sample simultaneously because interviewers are not required. They are relatively inexpensive compared with personal interviews, though they are not cheap. They can be filled out when the respondents have the time, so respondents are more likely to take time to think about their replies. They also allow respondents to collect facts that they may not be able to recall. Anonymity of respondents may result in them being more likely to provide sensitive or embarrassing information as well as reducing social desirability bias. Although the absence of an interviewer can induce respondents to reveal sensitive or socially undesirable information, this lack of personal contact can also be a disadvantage. Once the respondent receives the questionnaire, the questioning process is beyond the researcher's control. While mail questionnaires are highly standardized, this could be a disadvantage due to the difficulty in changing the format of the questions. If time is an issue, mail surveys may not be a good communication medium. Finally, mail questionnaires can be relatively long in length.
Answer to Question 2
Responses bias falls into four specific categories:
(1) Acquiescence bias: a tendency to agree with all or most questions.
(2) Extremity bias: results because some individuals tend to use extremes when responding to questions.
(3) Interviewer bias: occurs because the presence of the interviewer influences respondents' answers.
(4) Social desirability bias: may occur either consciously or unconsciously because the respondent wishes to create a favorable impression or save face in the presence of an interviewer.