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Related Concept Videos

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Hindsight bias leads you to believe that the event you just experienced was predictable, even though it really wasn’t. In other words, you knew all along that things would turn out the way they did. Can you relate this to the phrase "Hindsight is 20/20" now? 
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According to some social psychologists, people tend to overemphasize internal factors as explanations—or attributions—for the behavior of other people. They tend to assume that the behavior of another person is a trait of that person, and to underestimate the power of the situation on the behavior of others. They tend to fail to recognize when the behavior of another is due to situational variables, and thus to the person’s state. This erroneous assumption is...
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Humans are very diverse and although we share many similarities, we also have many differences. The social groups we belong to help form our identities (Tajfel, 1974). These differences may be difficult for some people to reconcile, which may lead to prejudice toward people who are different. Prejudice is a negative attitude and feeling toward an individual based solely on one’s membership in a particular social group (Allport, 1954; Brown, 2010). Prejudice is common against people who...
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Bias refers to any tendency that prevents a question from being considered unprejudiced. In research, bias occurs when one outcome or answer is selected or encouraged over others in sampling or testing. Bias can occur during any research phase, including study design, data collection, analysis, and publication.
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Biases can arise at various stages of research, from study design and data collection to analysis and interpretation. Recognizing and addressing these biases is essential to ensure the validity and reliability of epidemiological findings.Broadly speaking, biases in epidemiology fall into three main categories: selection bias, information bias, and confounding. A more detailed description of possible biases is:  
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Related Experiment Video

Updated: Jun 8, 2025

The Joint Effect of Social Comparison and Social Distance on Evaluation of Intertemporal Choice Outcomes in Event-related Potential Studies
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A Structural Description of Biases That Generate Immortal Time.

Miguel A Hernán1,2, Jonathan A C Sterne3,4,5, Julian P T Higgins3

  • 1From the CAUSALab, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA.

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Immortal time bias in survival analysis stems from selection or misclassification after treatment assignment, not the immortal time itself. Target trial emulation using longitudinal data synchronizes eligibility and assignment at follow-up start to prevent this bias.

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Area of Science:

  • Epidemiology
  • Biostatistics
  • Clinical Trials

Background:

  • Immortal time bias can occur in survival analyses due to post-eligibility information or post-assignment criteria.
  • This bias arises when follow-up begins at treatment assignment, but eligibility or treatment is determined later.

Purpose of the Study:

  • To explain the origins of immortal time bias in survival analysis.
  • To present methods for preventing immortal time bias, particularly through target trial emulation.

Main Methods:

  • Reviewing analytic approaches that prevent immortal time bias.
  • Utilizing longitudinal data to emulate target trials from the time of treatment assignment.
  • Explicitly defining eligibility and treatment assignment synchronization at the start of follow-up.

Main Results:

  • Selection or misclassification, not immortal time itself, generates bias.
  • Target trial emulation effectively prevents immortal time by aligning eligibility and assignment.

Conclusions:

  • Understanding the sources of immortal time bias (selection/misclassification) is crucial.
  • Target trial emulation is a robust strategy to mitigate immortal time bias in survival analyses.
  • Synchronizing eligibility and assignment at follow-up initiation is key to accurate emulations.