Nonresponse bias occurs when nonrespondents differ systematically from respondents. Which statement best describes this bias?

• A. Bias when nonrespondents differ from respondents
• B. Bias from measurement error
• C. Bias due to confounding
• D. Bias due to sampling frame not updated

Answer: (A)

Nonresponse bias happens when people who don’t participate in a study differ in systematic ways from those who do participate, and those differences influence the study’s outcomes. Because the missing data aren’t random, the estimates based on respondents can misrepresent the true population values. For example, if individuals with certain experiences or characteristics are less likely to respond, the calculated averages or associations may be biased upward or downward compared with the full population. This matches the idea that the bias arises from differences between nonrespondents and respondents. It’s not about errors in measurements (that would be measurement error), not about a confounding variable, and not about an outdated or incomplete sampling frame (that would be frame or coverage bias).