📌 *Bias*(systematic error) 🗝️ points *Selection Bias & Recall Bias - case control* *Berksonian bias - (Hospital patient data)* *Attrition bias - cohort(loss to follow up)* *Hawthorne bias - cohort ( attention - so changes habit)* *Pygmalion bias - (Researcher believes)* *Neyman/survival bias - Incidence Prevalence bias*