Flashcards in Survival Analysis Deck (24)

Loading flashcards...

1

## Survival Time

###
-Time to an event

-The time starting from a defined point to the occurrence of a given event

2

## Events for the end of survival time include

###
death

disease occurrence

disease recurrence

recovery

other experience of interest

3

## Special features in survival time data

###
-rarely normally distributed

-often skewed

-typically with many early events and relatively few late ones

4

## Censored Observations

### Those who have not yet reached the terminal event by the end of the study.

5

## In censored observations, why might information about a pt's survival time be incomplete?

###
-pt hasn't experienced event by end of study

-pt lost to follow up during study period

-pt experiences different event to make further follow up impossible

6

## Issues with censored observations in analysis

### these censored survival times will underestimate the true (but unknown) time to the event because it will occur beyond the end of the study.

7

## Kaplan-Meier Curve

###
-visualize estimate of survival over time

-shows probability of an event at a certain time interval

- x-axis for time, y-axis for 'proportion surviving'

-step function, as the cumulative survival remains the same until the day another person experiences the event

8

## Kaplan-Meier Curve Censored Data

###
x-axis: time

y-axis: 'proportion surviving'

-step function

-censored observations indicated on K-M curve as "tick marks"

-censored observations do not terminate the interval

9

## Kaplan-Meier Curve for 2 Groups

### Visualizes the difference between two survival curves. Can be used to compare treatments.

10

## Median Survival Time

### estimated as small survival time for which survival function is less than or equal to 0.5

11

## How can you estimate the Median Survival Time?

###
1. find the 50% mark on the proportion axis

2. drawing a horizontal line at 50% to find the crossing point with the K-M curve

3. drawing a vertical line at the crossing point down to the time axis to read time

12

## Mean Survival Time

###
-area under survival curve

-may not be best estimate for sample of survival times, highly skewed

-median typically better measure of central location than mean

13

## Hazard Rate

###
-measure of how often an event happens in one group compared to another

-in clinical trials, measures survival point at any point in time in a group given treatment vs control

-can be estimated as being a slope of a K-M curve

14

##
Interpreting Hazard Ratio

HR = 1

### the event rates are the same in both groups

15

##
Interpreting Hazard Ratio

HR >1

### the event rate in the treatment group is faster than in the control group

16

##
Interpreting Hazard Ratio

HR < 1

### event rate in treatment group is slower than in the control group

17

## Log-Rank Test

### Compares two or more samples with survival data in presence of censored observations

18

## How can a log-rank test fail

### if two curves cross (no statistical power)

19

## Assumption of Log-Rank Test

### Hazard Rates of the groups to compare must be proportional

20

## Limitations of Log-Rank Test

###
-We can only test one variable at a time

-can't control for potential confounders

-can't control for other potential risk factors

-can't include interaction terms

21

## Cox Proportional Hazard Model

### Most commonly used method comparing two or more samples with survival data in presence of censored observations

22

## T/F: Cox model can accommodate only one confounding variable

###
False

can accommodate any number of confounding variables

23

## T/F: Cox Model provides the estimate of Hazard Rate with its associated 95% Confidence Interval

### True

24