Part 3 · Epidemiology II — Trials, Bias, Causation and Screening
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| Error | Nature | Reduced by | Assessed by |
|---|---|---|---|
| Random (chance) | Sampling variability | Larger sample, more information | p‑values, confidence intervals |
| Systematic (bias) | Consistent distortion in one direction | Design and conduct, not sample size | Critical appraisal, sensitivity analysis |
| Confounding | Mixing of effects by a common cause | Randomisation, restriction, matching, stratification, multivariable adjustment | Compare crude and adjusted estimates |
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