Nonresponse Bias vs Response Bias
Both terms below come up in the same part of the course, and students mix them up. Here is each one defined on its own, side by side, so you can see where they part company.
Nonresponse bias
Collecting data and study design
Nonresponse bias occurs when people chosen for the sample do not respond, and those who do respond differ systematically from those who do not.
Nonresponse bias arises after the sample is chosen, when some selected people do not answer. For example, if a survey reaches a random sample but only the most satisfied customers reply, the results skew positive. The problem is not the missing answers themselves but that non-responders tend to differ from responders. Unlike undercoverage, which happens before contact, nonresponse occurs after people have been selected.
Response bias
Collecting data and study design
Response bias occurs when respondents give systematically inaccurate answers, for example due to confusing question wording or pressure to answer a certain way.
Response bias is about the accuracy of the answers people give, not about who is included in the sample. For example, a leading question such as asking whether people support a helpful new policy nudges respondents toward agreement. Sensitive topics can also cause it, since people may understate behaviors they think are frowned upon. Careful, neutral question wording and anonymity help reduce response bias.