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USMLE Step 2 (Subject) / Epidemiology & Stats (Lesson)
- Survival analysis Survival analysis is used to measure disease prognosis.Survival analysis is always prospective in nature:- Time-to-event analysis: Individual follow‑ups are done after the onset of a disease until a chosen endpoint (e.g., death, development of a particular complication) occurs or exposure to a risk factor to onset of disease.- Five-year survival rate: the percentage of patients with a particular disease who have survived for 5 years after the initial diagnosis Pitfalls of survival analysis: No prediction can be made about the average duration of survival in the case of subjects who did not die within the period of observation. (These subjects are called “censored cases”.)
- Power of a study Depends on: - Alpha level (statistical significance level): Lowering the alpha level (i.e., strengthening the significance criterion) decreases the power of the study - The magnitude of difference in the outcome between the study groups (i.e., a suble difference is more difficult to detect than a big difference) - Increasing the sample size increases the probability of detecting a difference in outcome between the study groups
- Maternal mortality rate Calculated by dividing the number of maternal deaths by the number of live births