# Survival Analysis (EPID 722)

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### Survivor function S(t)

probability that a subject survives longer than time t

### Characteristic of S(t) as Kaplan-Meier curve

vertical drop indicates an event, looks like stairs

### What does the log-rank test...test?

Are KM curves statistically equivalent?

### When to use KM curves w/ log-rank test

when predictor variable is:
categorical (placebo vs. drug) or,
only has a small # of values

### What do KM curves w/ log-rank tests suck at?

Continuous variables (e.g. gene expression values, whatever the **** that is)

### How do we do survival analysis on continuous variables? (e.g. white blood count, viral load, gene expression)

Cox proportional hazards regression analysis (Cox PH regression)

Cox can also do categorical data w/ dummy variables

And it "handles" censoring, whatever that means

### What is a hazard function? h(t)

h(t) is function of the probability of an event in a certain time interval GIVEN that the individual has survived up to time t

### What does it mean, proportional hazards?

hazards between group A and group B are proportional at all times

### What does the p-value of an HR signify?

probability that HR = 1

Example:

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