Cox Proportional Hazard Regression Flashcards

1
Q

What does log rank test do?

A

Tests if survival curves as the same for both groups.

2
Q

How do we test for confounders in survival curve?

A

Cox proportional hazard regression model. The log rank test is a crude association.

3
Q

What is the hazard rate ratio?

A

Estimates the hazard of one group compared to another.

4
Q

What is an assumption of the hazard rate ratio?

A

Proportional hazards: the difference between hazard in one group compared to another is constant over time.

5
Q

What is the equation for the Cox proportional hazards regression model?

A

h(t|X) = ho(t)e ^ (betaX)

6
Q

What do the pieces in a Cox regression model mean?

A

h(t|x) = Ho(t)e ^ (betaX)

h models the hazard
t is time
X is a given value of X
Ho(t) is the baseline hazard

7
Q

How is hazard modelled in a Cox regression model?

A

As a rate.

At time, t, for values of X.

Hazard is a function of time for some covariate X

8
Q

What is H0 in Cox model?

A

Baseline hazard when all coviariates = 0.

9
Q

What is E ^ βX in a Cox model?

A

E ^ β is the natural log of the hazard ratio; compares ratio by one unit in the value of X.
Difference in two groups at any point in time.

10
Q

What is beta in Cox model?

A

Represents the log hazard ratio of the outcome associated with a one unit change in X1.

11
Q

Give an example of log hazard.

A

21 leukemia pxs in placebo and 21 in treatment.
Outcome: time to cancer reccurence.
X1 is treatmentment group
X2 is log of while blood cell count.

12
Q

What is a model with those parameters with white blood cell as confounder?

A

h(t|x=1) = h0(t) * e^beta1(rx) + beta2*logwbc)

13
Q

What is a model with log wbc as effect modifier?

A

h(t|x=1) = h0(t) * e^beta1(rx) + beta2(logwbc) + beta3(rx*logwbc).

14
Q

What is e^beta1 for the following equation: h(t|x1=1) = ho(t) * e^beta1(rx=1)+beta2(logwbc=0)+beta3(rx=1*logwbc=0)?

A

e^beta1 is the log hazard ratio of time to cancer reccurence with a one unit change in X1 at fixed values of X2 and X3.

15
Q

What does the parameter estiamate of hazard show?

A

Hazard ratio comparing treatment to placebo group adjusting for log of wbc. Need to have e^rx estimate.

16
Q

What does Wald statistic say about hazard ratio?

A

Null: Hazard = 1
or
Beta = 0

17
Q

What is the code for hazard ratio?

A

proc phreg data = ander;
model survt*status (0) = rx logwbc /rl;
run;

survt is time to reccurence
status (0) is censoring variable
rl asks for confidence intervals around hazard ratio.