Questions tagged [proportional-hazards]

Proportional hazards is an assumption of the Cox proportional hazards model of survival analysis and some other models as well. The assumption is that a linear increase in the predictor will have a uniform multiplicative relationship with the hazard.

Filter by
Sorted by
Tagged with
0
votes
1answer
20 views

Cox proportional hazards model with inverse probability treatment weights: testing the Cox proportional hazards assumption

I have survival data of persons who participated/didn't participate in a health promotion program. To estimate the effect of the health promotion program on the hazard of mortality, I plan to use a ...
1
vote
0answers
12 views

Generating quantile-type predictions from Cox Proportional Hazards model

I am trying to generate quantile-type survival time predictions from a Cox proportional hazards model, similar to those generated from: ...
0
votes
0answers
21 views

Limit on number of features in Cox Proportional Hazards model with penalized spline

I am trying to fit a Cox proportional hazards model with penalized splines using the survival R package with the following, but it seems like I am hitting a limit ...
3
votes
1answer
40 views

How to interpret HR under non-ph

How do I interpret a HR under non-proportional hazards? Sounds silly, but I couldn't find a clear answer. Allison 2014 calls it a rough average. How is this average rough, and not a real average of ...
0
votes
0answers
13 views

Why is cox.zph splitting terms?

I'm using survminer to try to create a survival formula for a phenotype data set. ...
0
votes
1answer
20 views

Proportional hazards model with lognormal baseline hazard in R?

I would like to fit a proportional hazards model with log normal baseline hazard in R. I have found several options for the semiparametric Cox proportional hazards, but I have not found a package to ...
1
vote
0answers
12 views

How to go about interpreting time-varying co-variates in survival analyses?

I'm pretty new to stats.. been working with cox models and getting a little confused. 1) Why do they occur? 2) How might one interpret/clinically translate a time-varying co-variate for cox models? ...
3
votes
1answer
44 views

Cox proportional hazards. What does constant over time mean?

I am studying the Cox PH model. But there is one thing I cannot seem to wrap my head around. In the Cox PH model, we want the hazard ratio to be constant over time. But what is time in this case? ...
0
votes
0answers
19 views

Choosing a distribution for parametric hazard modeling

I have a question concerning determination of the baseline hazard function in a parametric survival regression such as Exponential, Weibull, e.g. Is there a way to determine which one is best? I have ...
2
votes
0answers
123 views

Error β€œsystem is computationally singular” when running cox.zph for a Cox Model

I have built an extended Cox Model in R, with time-dependent covariates, as described in this R vignette. I have built the model by running the following: ...
1
vote
0answers
18 views

How to prove that the likelihood of a proportional hazards with lognormal baseline model is log concave?

I want to fit a survival model using a proportional hazards assumption $$h(t) = h_0(t)\exp(x^T\beta),$$ where $$h_0(t) = \dfrac{\frac{1}{\sigma t} \phi \left(\frac{\log(t) - \mu}{\sigma}\right)}{\...
0
votes
0answers
20 views

Is this approach the right one in Cox with time-dependent covariates in R?

first of all I would like to thank you for reading my post. Then let me describe my situation: I'm trying to develop a Cox model with time-dependent covariates. I have a dataset of patients with ...
0
votes
0answers
36 views

Estimating age group specific hazard ratios from cohort data with left and right censoring

Background on the data: I have a dataset from a cohort of hundreds of thousands of individuals. Variables of interest included are: age at start of follow-up, disease endpoints, age at endpoint or ...
0
votes
0answers
16 views

How to interpret left and right censoring

I am fully aware that question regrading left and right censoring has been asked before. I will however post my own question, as I believe that its focus differs significantly. Here goes: I have a ...
0
votes
0answers
26 views

Violation of Proportional Hazards Assumption by a Continuous Variable

I'm constructing a multivariable Cox model and I am trying to assess whether the assumption of proportional hazards is valid using scaled Schoenfeld residuals (using ...
1
vote
1answer
45 views

Scaled Shoenfeld Residuals

When constructing a multi-variable Cox model, is it necessary to check the proportional hazard assumption for each covariate individually by first fitting a univariable model and checking the ...
2
votes
1answer
45 views

Is Cox Proportional-Hazards model appropriate for discrete time points

I'm dealing with medical data and I'd like to determine the dropout rates at about 10 different time points. Further I'd like to see the effect of various covariates on the dropout rates. Would a Cox ...
0
votes
0answers
35 views

Kalbfleisch Prentice survival calculation for Cox PH model

A method to estimate survival probabilities for a Cox PH model comes from Kalbfleisch and Prentice. It is explained in their 2002 book on page 114. They present a formula for the likelihood in terms ...
0
votes
1answer
44 views

How robust is coxph when the proportional hazards assumption is violated?

How robust is the coxph when I don’t have proportional hazards? How common is non prop hazards and how do I fix it? Does transforming variables help? Does non parametric survival analysis handle non ...
2
votes
1answer
44 views

Is the Breslow estimator over-adjusted?

In a proportional hazard model with a Breslow estimator, I wondered why do we adjust on covariates in the cumulative hazard and in the model. On these few lines from Xia et al.[2], we can see that ...
0
votes
0answers
28 views

Survival analysis with two events

Suppose we have a cohort of subjects, we have followed them up over a period of 10 years and several subjects develop either of two complications of interest (A and B) that are complications as a ...
1
vote
1answer
141 views

Cox PH - R 'rms' package - Concordance (Train, CV & Test)

Please could someone verify if my methodology for calculating these three versions of concordance are correct when using the rms package? I have really struggled to ...
1
vote
1answer
148 views

Checking PH assumption using scaled Schoenfeld residual tests

My cox model violates the PH assumption (according to cox.zph test), and I'm trying to interpret the scaled Schoenfeld residual plot, but I've never seen a plot with points lying in such a flat manner....
0
votes
1answer
33 views

Cox Proportional Hazards - Survival Function Estimation (on new data)?

I understand that the relationship between the hazard function, the baseline hazard function and the covariates is the following: $$ ln(\frac{h(T)}{h_0(T)}) = \beta_1 x_1 + \beta_2 x_2 + \dots + \...
3
votes
1answer
130 views

Case-Cohort analysis in R

I am attempting to conduct a Case-Cohort analysis with Cox's Proportional Hazards Model. The data set looks similar to the one below: ...
0
votes
0answers
32 views

Different results for Cox regression

I am trying to get my head around Cox regression. I found quite a good paper on the subject by R. Tibshirani: A plain man's guide to the proportional hazards model. On page 67 he gives a toy example, ...
0
votes
0answers
41 views

Why is the exponential function used in Cox regression?

I am trying to get my head around Cox regression. I found quite a good paper on the subject by R. Tibshirani: A plain man's guide to the proportional hazards model. On page 66 he states: For ...
0
votes
1answer
41 views

Continuous Variable No Longer Follows PH Assumption When Categorized

I am creating a cox regression model with multiple covariates. I have two models: model A contains my variable of interest in its original continuous form, and model B contains my variable of ...
1
vote
2answers
78 views

Expressing a hazard function with a Cox proportional hazards model

I'm trying to wrap my head around Cox models as well as how to express them in the form of hazard functions when you have both categorical AND numeric covariates. I need some assistance with this ...
1
vote
0answers
44 views

Hazard ratio endpoint vs Odds ratio

This study (https://academic.oup.com/cid/article/65/1/100/3097834) seems to conduct a cox proportional hazard regression on survival data, but reports hazard ratios for 30- and 90-day mortality: ...
1
vote
1answer
93 views

What are the hazard ratios in this plot referring to?

With the following code in R, I created this graph: ...
1
vote
1answer
464 views

Schoenfeld test (cox.zph) shows no covariate violates PH assumption but global test suggests whole model does (p<0.001). What to do?

Using cox.zph (part of the survival package), I find that no covariate violates the PH assumption in a Cox regression model (p > ...
2
votes
1answer
131 views

How to model the Hazard Rate?

I'm interested in modeling the Hazard Rate $\lambda$ from a Survival dataset so I can calculate the Cumulative Distribution $F(t)=1-e^{-\lambda t}$ but I'm not sure how to go about computing $\lambda$...
0
votes
1answer
100 views

Is the Cumulative Hazard Function simply estimated using the Empirical CDF?

I'm just starting to learn about Survival Analysis and I understand the theoretical proofs but I'm still unclear about how to do some of the estimations practically.
0
votes
0answers
18 views

Cox Proportional Hazard calibration with same it's meant to predict

I want to model time to churn with a Cox Proportional Hazard model and use it to predict people likely to churn. The question I have is how valid is to calibrate the model with the same people I want ...
1
vote
0answers
35 views

Predicting survival probability at a future time for proportional hazard model

I have a Weibull proportional hazard model with fitted parameters $\lambda$ and $k$ and a time dependent covariate $x(t)$ with fitted coefficient $\beta$, such that the hazard function is given by, $...
0
votes
0answers
35 views

Prediction of survival time using cox regression in R

I'm aware that we can get survival function and probability in R but is there a way to predict survival time given it is Cox regression
0
votes
0answers
11 views

Likelihood function for a unit $i$ with death at time $t_{i}$ and non - death at time $t_{i}$

The survival function with respect to time is defined to be $S(t) = 1 - F(T) = \int_{t}^{\infty}f(x)dx$ With a bit of algebraic manipulation, one arrives at the time dependent hazard rate ...
0
votes
1answer
196 views

Cox regression model - testing the proportionality assumption for an interaction term?

I'm interested in testing sex differences in the outcome Y (e.g., mortality), and if there are sex differences in the effect of BMI on mortality. I planned to use a Cox regression model primary<-...
0
votes
0answers
48 views

Why is my output for nominal_test incomplete?

I am currently using the nominal_test function, in the ordinal package, to test for the proportional odds assumption but have encountered a problem. Here is my code: ...
1
vote
0answers
28 views

Test assumption of common baseline - Adersen-Gill Cox regression?

I'm running a Andersen-Gill recurrent (multiple events) cox model and I want to test the assumption of common baseline across events. Is this as simple as entering 'event' into the model and checking ...
1
vote
1answer
465 views

What does 'km' transform in cox.zph function mean?

I'm trying to understand how cox.zph function in r programming language works and I find myself not knowing what km transform ...
1
vote
2answers
525 views

Interpreting hazard ratios in stratified models

I am unsure how to interpret hazard ratios from cox-proportional hazard models that include 1 or more stratified terms. For example, say I run a cox regression with treatment as a covariate and ...
0
votes
1answer
41 views

Survival Analysis - 30% right censored data

Just looking for some clarity regarding time-to-event (death) data when there is a large proportion of right censored data (lots of survival). Is this a serious problem for a proportional hazards ...
0
votes
1answer
87 views

Checking PH assumption for a time dependent (T_COV) variable in a Cox PH-regression: with or without the original covariate in the regression?

I am performing a cox proportional hazard regression on survival, in a sample in which almost everyone dies in the follow up period. I have little knowledge on statistics in general but i am reading ...
0
votes
2answers
344 views

Schoenfled Residua test shows proportionality hazard assumptions holds but Kaplan-Meier plots intersect

"If Kaplan-Meier plots cross each other then proportional hazard assumption does not hold". The issue I am facing is that I got the Kaplam-Meier plot(bleow). We can clearly see that it is overlapping. ...
0
votes
1answer
101 views

Obtain hazard ratio from other hazard ratios

Given a hazard ratio($HR$) as $$𝐻𝑅_{b}=β„Žπ‘Žπ‘§π‘Žπ‘Ÿπ‘‘(b)/β„Žπ‘Žπ‘§π‘Žπ‘Ÿπ‘‘(a)$$ and another hazard ratio as $$𝐻𝑅_{c}=β„Žπ‘Žπ‘§π‘Žπ‘Ÿπ‘‘(c)/β„Žπ‘Žπ‘§π‘Žπ‘Ÿπ‘‘(a)$$ How can we obtain the hazard ratio between $b$ and $c$ ...
1
vote
1answer
322 views

Hazard ratio for more than two groups

Consider the line of code below for implementing Cox model in R and finding the hazard ratio: fitcox <- coxph(Surv(Survival,Death) ~ clusters, data = data) ...
4
votes
2answers
126 views

How to calculate Hazard ratio if there are more than two Kaplan-Meier curves

A population was sub-typed into 4 groups and Kaplan-Meier curves were plotted. If there were only two survival curves then the hazard ratio would be the hazard of one group divided by the hazard of ...
1
vote
0answers
220 views

Violation of proportional hazard assumption with big sample size - how to correct for it?

I am looking at a sample of about 95,000 firms in Switzerland and I want to find out if having an external auditor (such as PwC, KPMG, EY) reduces the likelihood that a firm goes bankrupt. In ...