Which statement best describes survivor bias in this context?

• A. Short-term users are more compliant
• B. It inflates sample size
• C. It biases results toward no effect
• D. Long-term users are healthier

Answer: (D)

Survivor bias happens when you analyze only the people who stay in a study or continue with an exposure over time, leaving out those who dropped out or died. In this setup, the individuals who remain long-term are often healthier, more resilient, or better able to tolerate the exposure. That means the group of long-term users looks healthier simply because the less healthy ones left earlier, not because the long-term use itself is beneficial. So the statement that long-term users are healthier captures the essence of survivor bias: the remaining sample over time is biased toward better health.

The other statements don’t describe this bias as well. Short-term user compliance speaks to adherence behavior, not survival in the study. Claiming the bias inflates sample size isn’t accurate—dropouts typically reduce the effective sample. Saying the bias biases results toward no effect contradicts the typical direction, since survivor bias often makes outcomes appear more favorable (or more extreme) than they truly are.