• Under-coverage: The sample fails to represent the entire population because complete information about the population is inaccurate or unavailable.
• Nonresponse: Selected individuals fail or refuse to respond.
• Response Bias: The response given by the respondent may have been influenced by improperly or poorly worded survey questions or by the behavior of the interviewer. Response bias can occur because respondents may lie when presented with questions of a personal nature or questions regarding illegal activity.