# Radiation Oncology/Survival analysis

## Experimental DesignsEdit

## Survival AnalysisEdit

- Survival analysis is a branch of statistics for analyzing the expected duration of time until one or more events happen, such as death in biological organisms and failure in mechanical systems
- This topic is called reliability theory or reliability analysis in engineering, duration analysis or duration modelling in economics, and event history analysis in sociology
- Survival analysis attempts to answer certain questions, such as what is the proportion of a population which will survive past a certain time? Of those that survive, at what rate will they die or fail? Can multiple causes of death or failure be taken into account? How do particular circumstances or characteristics increase or decrease the probability of survival?

**Proportional Hazard Model**

- Proportional hazards models are a class of survival models in statistics
- Survival models relate the time that passes, before some event occurs, to one or more covariates that may be associated with that quantity of time
- In a proportional hazards model, the unique effect of a unit increase in a covariate is multiplicative with respect to the hazard rate
- For example, taking a drug may halve one's hazard rate for a stroke occurring, or, changing the material from which a manufactured component is constructed may double its hazard rate for failure

- Other types of survival models such as accelerated failure time models do not exhibit proportional hazards
- The accelerated failure time model describes a situation where the biological or mechanical life history of an event is accelerated (or decelerated).