# Cox Proportional Hazard Regression Flashcards

What does log rank test do?

Tests if survival curves as the same for both groups.

How do we test for confounders in survival curve?

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

What is the hazard rate ratio?

Estimates the hazard of one group compared to another.

What is an assumption of the hazard rate ratio?

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

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

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

What do the pieces in a Cox regression model mean?

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

How is hazard modelled in a Cox regression model?

As a rate.

At time, t, for values of X.

Hazard is a function of time for some covariate X

What is H0 in Cox model?

Baseline hazard when all coviariates = 0.

What is E ^ βX in a Cox model?

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.

What is beta in Cox model?

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

Give an example of log hazard.

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.

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

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

What is a model with log wbc as effect modifier?

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

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)?

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.

What does the parameter estiamate of hazard show?

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