[Cox proportional hazards regression][1] is a very popular, semi-parametric method for survival analysis.

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R: how to plot a cox regression model survival curves (treated vs control curves) using ggplot2? [migrated]

I have a cox model in R that shows time to diabetes. The formula is: ...
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29 views

Survival Curve vs Cox PH hazard levels discrepancy

This is a very high level question, hope it's not too general for this forum: Is it possible to have a greater risk (hazard) for a factor variable in a COXPH regression for one level against another ...
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43 views

Survival Analysis: Cox Proportion Assumption

I know i'm missing something here, please help me understand the cox proportion assumption. What is the point of having a hazard rate function over time if it first has to meet the cox proportion ...
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Modeling mortgage prepayment behaviour using survival analysis

I am doing a study of prepayment behaviour on mortgage loans where the partial prepayment (curtailments) are very frequent and sort of normal behaviour as there are no penalties for such events. As a ...
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what to do when proportional assumption is not met in stata

I have built a Cox multiple regression model. When I tested the proportional hazard assumption using estat phtest command, I realized the PH assumption is not met. In this case, what is the next step? ...
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8 views

Interpretation of an interaction term in survival analysis

I'm struggling with an interpretation for an interaction analysis. In the univariable Cox analysis, the HR for variable 1 is 1.03 (95%CI 1.02-1.04) and for variable 2 is 0.37 (95%CI 0.26-0.55). In ...
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Issues with showing total N and missing data, total observations on Cox model

I'm trying to get an article which tries to assess if there was a higher risk of a condition being longer in a year when compared to a previous year. I' m not getting a lot of help, so I sincerely ...
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Can I use Cox PH regression to capture exogenous effect?

Can I use Cox PH regression where I have 'subjects entering the study at different point in calendar-time' and 'the covariates are exogenous which varies with calendar-time' ? Eg. To study the effect ...
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Remedy for failure to satisfy Proportional Hazards Assumption?

I'm tasked to perform a Cox Proportional Hazards Regression on our company data. After preparing the data, I started testing the proportional hazards assumption which, according to my readings, will ...
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Poor survival analysis model fit with Gronnesby and Borgan

I have been experiencing issues with model fit. In my example, I have set up a time-varying (counting method) survival analysis model (Cox regression with ...
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26 views

How do I get interval-specific survival rates from an Andersen-Gill model?

I am using coxph in the survival library to create Andersen-Gill models. I am interested in getting interval-specific survival rates for my data. For instance, I ...
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Back transformation for log-transformed variables in Cox regression

I have to perform a meta-analysis. My problem is that in a number of studies, the HRs for the explanatory variable are reported for the log transformed variable; in addition in one of the ...
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19 views

Competing risks using crr in R with time-dependent dummy variable indicating treatment

I am trying to incorporate a time-dependent dummy variable for treatment using crr in the cmprsk package in ...
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1answer
26 views

p-values in a Cox-Regression model

I have a question regarding the output of a Cox-Model I obtained by stepwise model selection. My model includes now some variables with a p-value below 0.05 and some above 0.05. Since I want to ...
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19 views

Standard errors and confidence interval in cox regression model validation using RMS package

I am using RMS package of R to validate cox regression model with bootstrap. Please see the sample code below. I have three questions: (1) How do I request the standard errors and/or confidence ...
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22 views

confidence intervals for cox proportional hazards with 0 events in one treatment arm

We are performing a multivariate cox proportional hazards analysis with 6 covariates. Two of the covariates (Pre_ASCT_response2 and NGS_graft_MRD2) are binary covariates with 0 events in one ...
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Basic question regarding construction of likelihood function from a Cox PH model

I have a simple question (which I sense may have a complicated answer) regarding the fundamental logic concerning how the likelihood function from a Cox PH model is derived. Assuming the $i^{th}$ ...
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34 views

Why use ln-ln plot in proportional hazard test?

I recently began studying survival analysis and there is something I am curious about. Why do we prefer to use the ln-ln survival curve rather than the survival curve in a proportional hazard test? ...
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34 views

How to calculate gradient of partial log-likelihood function in Cox proportional hazards model?

Is there any existing function in R or package that calculates gradient of partial log-likelihood function in Cox proportional hazards model? I've tried myslef on this question (How to compute ...
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How to compute gradient of partial log-likelihood function in Cox proportional hazards model?

The partial log-likelihood function in Cox proportional hazards is given with such formula $${}_{p}\ell(\beta) = \sum\limits_{i=1}^{K}X_i'\beta - \sum\limits_{i=1}^{K}\log\Big(\sum\limits_{l\in ...
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How to compute partial log-likelihood function in Cox proportional hazards model?

The partial log-likelihood function in Cox proportional hazards is given with such formula $${}_{p}\ell(\beta) = \sum\limits_{i=1}^{K}X_i'\beta - \sum\limits_{i=1}^{K}\log\Big(\sum\limits_{l\in ...
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How to “deal” with functional form of covariate?

I am doing cox regression analysis and am confused with the different of implications of functional form using cumulative martingale residuals and use of cumulative residuals to assess ph assumption. ...
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25 views

Age at entry point as a covariate in cox regression

Patient Age will almost always violate the PH assumption since it is a time-vayring variable, especially in long follow-ups and higher mean sample ages. Do we have to account for that (ie including ...
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Interpreting interaction terms in Cox Proportional Hazard model

I am new to survival analysis, so forgive me if this questions is stupid - but I couldn't find the answer anywhere else. We are looking at readmission to a treatment program, which is defined as ...
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44 views

How to interpret the Accuracy and Importance in RandomForest test from Cox regression models

I am trying to use random forest to show the results from Cox regression analysis. I have 757 samples with complete follow-up data (456 cases and 301 control). The case is defined as ...
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NA values for coefficients in Cox proportional hazards model

I'm doing a cox regression analysis. My model is given by ...
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Right-censored independent variable in Cox/logistic regression

I have a right-censored continuous independent variable that I want to include in a Cox regression. The variable is a physiologic test which is capped at a certain time, say 120 seconds, due to safety ...
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Late Cross of Kaplan-Meier Curves - Does it matter?

Does a late cross of Kaplan-Meier curves necessarily violate the proportional hazards assumption? I have seen it argued (e.g. here) that it matters less if the curves cross late in the graph because ...
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22 views

Risk estimation in Cox survival analysis

I'm trying to compare two Cox models (a model with a new biomarker with a baseline model without that specific biomarker). More specifically, I'm trying to calculate the categorical NRI (Net ...
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59 views

Why are correlated observations not an issue in Cox regression with time-dependent covariates?

In the extended Cox model we can easily include time-dependent covariates $X(t)$. If we use counting process notation, this will result in multiple records per patient. Each record consists of (start, ...
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31 views

How to request predicted points for each patient based on nomogram in RMS?

I am generating nomogram for a survival analysis project using RMS package of R. A PI of the project would like to have predicted points for each patient in the sample predicted by the nomogram. Is ...
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23 views

How to interpret hazard ratios for time-segmented variables?

I'm constructing a Cox regression model where patients were randomised to treatment or placebo, and then had certain continuous covariates measured at multiple time points through the course of the ...
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How should i set up a cox regression using the following variables? SPSS

I am completely unfamiliar with Cox regressions and most statistical analysis. My advisor for my undergraduate research project suggested that I use this type of regression on my data. I have already ...
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Modelling retirement of employees by age where only data of very view years are available

We want to model the retirement of employees. We have data on a yearly base for about 20,000 employees by age and some other properties. There are two questions: Suitable Approach In most cases we ...
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Building Cox Proportional Hazards Models and Getting Accurate Confidence Intervals

I have 4000 data records of survival data and 100 potential predictors/variables. My aim is to obtain the most important variables describing this data. Since complete data records are needed I ...
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75 views

Interpretation of Confidence Intervals using Cox proportional hazards regression model (coxph)

I am using the coxph function to model a Cox regression. By using stepwise BIC selection I obtained an model with 6 variables. One of the variables I had to transform using the logarithm to make it ...
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Distribution of weighted Cox regression coefficients

I know that under typical conditions, the coefficients of a Cox model, the coefficients are asymptotically normally distributed. I plan to weight my Cox model by inverse probability of treatment ...
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Model selection with cox proportional hazard mix models (cox.me)

I am using a cox proportional hazards model to run a survival analysis in R. The analysis involves analyzing which biochemical markers predict mortality in buffalo. I am using id as a mixed effect to ...
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Is Cox regression with a time dependent covariate appropriate for survival time given number of hospital admissions?

II've got a bunch of data on hospital admissions and I'm trying to establish if the number of admissions somebody has had is associated with survival time. I also wish to control for a bunch of other ...
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Cox proportional hazards - risk increase for a given increase in predictor variable

I am trying to assess the predictive properties of a variable for an event. The following output from R, describes the model: ...
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32 views

Survival analysis no one failed during the period of the study

I'm trying to analyze data where I found that no one failed during the period of the study. This is the Error I got, as I gave the command. ...
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Censoring for events that don't occur

I have data on when the time between two events A and B. However, I am assuming if the time between them is more than 5 hours then the two events are unrelated and so we assume that on these occasions ...
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How is stratifying by X in proportional hazards model different from adjusting for X?

I'm familiar with stratification vs adjustment in linear regression. I'm wondering if stratification vs adjustment in CPH is conceptually similar? The stratification variable I have question about is ...
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207 views

Interaction effects in Cox model (continuous, dichotomous, and categorical variables)

I get a couple of puzzling results in my (repeated event) cox model when I introduce interaction effects. I will here pose several questions about interaction effects (in survival analysis context) in ...
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179 views

Precisely how does R's coxph() handle repeated measures?

Context I'm attempting to understand how R's coxph() accepts and handles repeated entries for subjects (or patient/customer if you prefer). Some call this Long format, others call it 'repeated ...
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How to interpret coefficients of nonlinear covariates in cox model?

My cox model has 4 covariates in which I found that 2 covariates are nonlinear effect on hazard. Then, I tried to fit these 2 covariates with quadratic and square root form. But I am confused about ...
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49 views

Correct use of variables in Cox Regression

I have a sample of 3000 patients and, for each of them, I know the number of years they lived. I was able to monitor these patients over 10 months (at a random time of their life). So I have left and ...
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65 views

Cox regression: multiple observations and time-varying covariates (Stata)

I have two questions with regards to cox regression and fixed/time-varying predictors in Stata. I am using cox regression for time-to-first-failure analysis. Using the 'stset' command I have been ...
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43 views

Extended Kaplan-Meier for survival curves from Cox PH model with time-varying covariates?

I am interested in using a proportional hazards model with external time-varying covariates for the purpose of predicting future event probabilities. Since extracting survival curves with ...
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What test shall I use to validate the use of a certain score to predict my outcome in a survival analysis?

I validate usage of a clinical cardiovascular score to predict the risk of dementia using data from a longitudinal study. Therefore, my outcome is binary (dementia yes or not) and the independent ...