RESS - Survival analysis

Question 1

What kind of data is required in survival analysis?

Answer 1

1. The time a person enters the study

2. The time the person leaves the study (may be due to death; asking to leave; losing track of person)

Question 2

What is ‘censoring’ in survival analysis?

Answer 2

If a person leaves the study before the event occurs or enters the study after the start of the study

Survival data may be right or left censored:

Right - people in the study did not reach a failure before the end of the study e.g. a study looking at a new drug to treat HIV, right censored data will occur if the study participants die of other non-AIDS causes

Left - not certain what happened to people before they entered study e.g. people with the disease when study starts

Question 3

Define: survival function

Answer 3

The chance of survival until a certain time

Question 4

Define: hazard function

Answer 4

The chance of instantaneous failure at any one time

Question 5

What does the Kaplan-Meier plot show?

Answer 5

Survival as a series of steps

It steps down every time a failure is observed

Question 6

What tests can survival data be examined with?

Answer 6

Log-rank test

Cox proportional hazards modelling

Question 7

What does the log-rank test compare?

Answer 7

The survival functions between 2 groups