This document discusses nonresponse bias in surveys and methods for assessing its impact. It begins by explaining why low response rates can undermine survey validity and introduces techniques researchers have used to increase response rates over time. However, it argues that response rate alone is not a good indicator of bias; more important is understanding if and how nonrespondents differ from respondents. The document then presents the Nonresponse Bias Impact Assessment (N-BIAS) framework, which involves using multiple techniques like archival analysis, follow-ups, wave analysis, and others to evaluate nonresponse bias in a given study.