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Case-Control Imbalance

Definition
AI-generated

Case-control imbalance means a binary-trait study has far fewer cases than controls, often by orders of magnitude in biobank-scale analyses of rare diseases.

Topics
Epidemiology
Synonyms
Class imbalance
Related
Case-Control Study Effective Sample Size Firth Regression

Why it matters in GWAS

Severe imbalance reduces effective sample size and can inflate type I error if the analysis method is not designed for it. This is why large binary-trait GWAS often use methods such as SAIGE, saddlepoint approximation, or Firth-style fallback rather than plain score or Wald tests.

Example usage

"Because the phenotype had 1,200 cases and 180,000 controls, we used SAIGE to handle case-control imbalance in the rare-variant scan."

Case-Control Study Effective Sample Size Firth Regression Minor Allele Count (MAC) Odds Ratio (OR) Scalable and Accurate Implementation of Generalized Mixed Model (SAIGE) Saddlepoint Approximation
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References

  • Zhou W, et al. (2018). Efficiently controlling for case-control imbalance and sample relatedness in large-scale genetic association studies. Nat Genet. https://doi.org/10.1038/s41588-018-0184-y
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