BIAS Lead-time bias Measurement biasObserver bias Recall bias Selection bias Hawthorne effect
Lead-time: when an intervention looks better because it diagnoses the disease earlier. survival looks longer but actually the same. Measurement bias: poor data Observer bias: study not blinded Recall bias: study participants answer questions affected by other exposures. High in retrospective studies Selection bias: not properly randomized/ or not retained. ex- treatment group picked 2/2 severity of disease Hawthorne effect: when people know they are in the study