# Questions tagged [cox-model]

Cox proportional hazards regression is a semi-parametric method for survival analysis. No distributional form needs to be assumed, only that the effect of one-unit increase in a covariate is a constant multiple.

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### Am I able to calculate the p-value from hazard ratios and effect size?

I ran a Cox proportional-hazards (coxph) model on my data, which contains individuals with either a disease status1 or disease status2, and they have been administered either treatment A or treatment ...
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### Multi-centre survival analysis

I have question regarding survival analysis. I am looking at observational studies comparing patient survival who received treatments A or B at different centres (>10), for the same condition and ...
1 vote
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### Is it possible to use my dataset for survival analysis, if so, how should I adapt it?

I'll try to summarize my situation as best as I can first. I'm doing a project in which we're trying to do a prognostic model on a specific disease to determine the risk of an outcome happening to ...
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### How to interpret the schoenfeld residuals plot

I want to check the proportional hazard assumption. I used both test using cox.zph() in R and schoenfeld residuals plot using hggcoxzph(). I want to know if the plot is fine and how I can interprete ...
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### How do survival models "account for censoring"? (Do they?)

Background I'm teaching an intro stats class in our social / health sciences department and I'm finding myself tripped up on something I'd always taken for granted: namely, the claim that survival ...
1 vote
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### Survival analysis interaction interpretation: interaction is insignificant, but pairwise comparison does hold significance

I'm new with survival analyses, and have been breaking my head over this for a while, so I hope someone can explain this in a simple manner: Variable HR Gender(Female) 1.391* Treat (Yes) 0.544*** ...
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### Joint Models - compound poisson

Let's say I have a longitudinal process that I can dicotomize as 0/1 depending on a literature established cutoff. I would be interested in modelling the number of events occurring for each individual ...
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### Survival Analysis with Time-Varying Covariates and Numerous Cross-Sectional Units

I am seeking clarification regarding how to set up data for survival analysis in R with both time-varying covariates and numerous cross-sectional units. I come from a Stata background and am ...
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### How to formulate and simulate data from an accelerated failure time model?

I understand that an accelerated failure time model can be conceptualized as a cox model which includes covariates whose effects depend on actual time, so the convenient expression of the partial ...
1 vote
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### Survival analysis of a stratified case-cohort study in R

I am trying to perform a survival analysis for a stratified case-cohort study (1:2) where cases are patients with distant recurrence (DR) and the cohort is composed by patients without distant ...
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### Martingale residuals in Cox PH model for categorical variable

I understand that for continuous data, martingale residuals can be used to assess the linearity of the variable, but if it's a categorical variable (2 levels) is there any interpretation that comes ...
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### Categorical Variables Cox Proportional Hazards Model SPSS

How can I stratify individual categories for a variable when doing Cox models to see if a particular category within the variable is a significant predictor in SPSS? For example, the variable can be ...
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### Getting multiple states in coxph output R

I'm trying to do a cox-regression with a time-dependant covariate. The time is measured in hospital days (0, 1, 2, 3, 4). And each day has a unique entry for the continious variable VAR1. I've created ...
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### Cox Proportional Hazards regression where event is most likely to occur at set intervals

I'm interested in evaluating the effect of various factors on the lifespan of borrower-lender relationships using a Cox Time-Varying Proportional Hazards regression. However, as the relationships we ...
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### Adjusting for drop-outs in survival analysis when all dropouts have time = 0 and event = 0

I have data where participants were assessed at two timepoints ; baseline and follow up. At baseline, participants were categorised based on presence of a marker (yes = 1, no = 0). At follow-up, ...
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### Inverse probability weighting for right censored data in cox regression

I have data from a prospective study with two measurements per participant (baseline and follow-up). I am interested in whether a cut-off (binary) obtained at baseline predicts disease development at ...
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### Cox regression hazard ratio (group 1 vs. group 4) changes calculation changes after combining group 2 and 3?

I am working on a project which involves fitting a Cox proportional hazard model to a time to event situation in SAS. We have the variables: y - event or censor (0/1) timeto - time to event y x - ...
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### Cox model stratification

I am confused about stratifying on a variable in Cox models. I think $e^{\beta_1}$ still represents the hazard ratio for somebody with $x=2$ vs $x=1$, but I don't quite understand how it's still a ...
1 vote
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### Hazard ratio and relative risk (or odds ratio) in case of very few event/censoring times

As far as I understand relative risks and hazard ratios are very similar concepts (although this paper seems to disagree). The advantage of hazard ratios is the inclusion of temporal information. I ...
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### Interpreting results of likelihood test in cox model comparison

I am utilizing a cox model for time to event analysis. I have a continuous predictor, that appeared to violate the linearity assumption. I then re-did my model with a spline function, and compared my ...
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### Question about censoring impact on training (survival analysis)

I have a question regarding the impact that censoring has on the predictions from a survival model. For example, let's say we are trying to estimate the risk a client has to churn in the next 1 month ...
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### Assessing violations of the Cox proportional hazards assumptions

Cox models assume proportionality. These assumptions can often be formally tested (an example in R is cox.zph from the ...
1 vote
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### Is is acceptable to use cox proportional hazard regression when time-to-event is a discrete, numeric variable?

I recently submitted a paper where I performed a cox proportional hazards regression model modelling the effect of group allocation in a randomised controlled trial on treatment retention. The event ...
1 vote
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### Hazard ratio with time-varying covariates

I am confused about time-varying covariates in Cox models. I believe this refers to the fact that in the normal situation, you can calculate a hazard ratio for $X$, assuming $X$ for an individual is ...
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### How to interpret the Wald Chi-square test for the frailty term in a mixed-effects Cox survival model?

Background I'm fitting a Cox model to assess the relationship between treatment (binary) and time-to-event (event is also binary) while also controlling for 3 or 4 covariates. Because I want to ...
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### Joint Models - Time specification in longitudinal and survival submodels

A quite general question. When I jointly model time to event data and longitudinal process with Joint models, looking at math behind it, it seems to me that the times to event outcomes and times of ...
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### Time varying covariate is polytomous for cox proportional regression, how to deal and interpret?

I am trying to conduct a cox proportional hazard, after I checked the assumptions, it turns out that interaction exists. So, I have to put an interaction into the model. But the time varying covariate ...
1 vote
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### How to fit parametric distribution to baseline hazard in cox PH model

I develop Cox PH model with time-varying covariates to predict marginal probability of some event. The time frequency is measured in months and I have observations since 3 months to more than 160 ...
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### Can we remove group with no event from Cox Regression model?

I had a similar data set to what I posted yesterday. I run a Cox-regression model to find the Harzard Ratio between group of interest. I had one group having no event and once that group was set to ...
1 vote
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### Cox PH controlling for multiple events

I'm working on a cox proportional hazard analysis in R using the survival package. I´m analysing covariate effects on fish movement within a study area. The study area is divided into two zones ("...
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### Cox Proportional Hazards : Why not "Cox Proportional Survival"?

Recently, I thought of the following question: We are often taught about a "Cox Proportional Hazards Model" - this is able to model the hazard between different cohorts of patients, assuming ...
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### Sample size calculation for Cox regression with time-varying exposures

I'm involved in the design of a longitudinal observational study investigating a relationship between the use of a drug and a binary outcome. Participants are enrolled when at risk of the outcome, ...
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### How does the lifelines package calculate the CoxPHFitter log-likelihood? [duplicate]

I'm looking for the equation that how the lifelines package calculates the log-likelihood of CoxPHFitter. I read the lifelines documentation but cannot find where is it. Any help would be appreciated!
1 vote
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### How to deal with left truncation in cox model in R

I have a longitudinal data with 8 follow-ups. My aim is to see the effect of a disease on ability decline at old age. In my study, I have sibling pairs, one with disease (1) and one without disease (0)...
1 vote
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### Comparing goodness of fit across parametric and semi-parametric survival models

I've been learning about time-to-event analysis and playing with open datasets + fitting various Cox and parametric models for practice. Other than by visually inspecting the estimated survival curves ...
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### Is it possible to estimate IPTW in two different subgroups to evaluate interaction? (Subgroup Balancing Propensity Score?)

This questions needs a toy example to be explained. I apologize if the question is not clear. Suppose we have an observational study in which we want to evalute the association between exposure to ...
1 vote
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### Calculate time at risk using cox proportional hazards

Can you calculate the time at set risk from proportional hazard models? Say I've got my model built for the whole population. The risk of developing an event in one year is 5%. After stratification, ...
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### Compare two groups in Cox Proportional Hazards model

I have a Cox Proportional Hazards model and I'd like to check if there are statistically significant differences between ECOG groups 1 and 2 (HR: 1.32 vs HR: 2.19). I have thought of doing a paired t-...
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### How to test overlapping confidence intervals to see a significant difference between groups in a COX propotional model

Cox proportional models have been done with this result. The two groups (C, B) had overlapping confidence intervals, while the p-value was significant at p<0.001. I have used this code to get the ...
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### Difference between "predict" and "predictSurvProb" R functions

I am trying to predict survival probabilities after estimating a Cox model with coxph in R . I am aware of 2 functions: predict ...
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### Can I use non-stationary variables in forecasting problem

I want to build survival analysis model (Cox PH) with time-varying covariates. Time-varying covariates are macroeconomic variables. Therefore, they are same for each individual at the same calendar ...
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### Why R survAUC::AUC functions require both training and test data?

I am familiar with binary classification models, where the AUC is the metric from the area under the specificity-sensitivity curve, it indicates the performance on a dataset. Now, I'd like to assess ...
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### Time-Varying Covariates in a Cause-Specific Hazard Regression

I'm estimating a cause-specific hazard function using the coxph() function in R. This the first time I've run such an estimation. In performing model diagnostics, ...
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### Should the N events that is output by coxph when using counting process format be the same as the N events prior to reformating?

I am performing a coxph analysis using time dependent and time independent covariates. I have formatted my data into the counting process form to allow for time dependent covariate. Prior to changing ...
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### IPTW in Cox Regression model using the WeightIt package - Question on ATT vs. ATE interpretation

I am currently trying to perform some IPTW adjustment in the context of Cox Regression models. I was interested in expanding my understanding of the differences between ATE vs. ATT estimation. I've ...
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### When having non-proportional hazards, should I use stratified Cox by time or Logrank tests within periods?

My data have non-proportional hazards with clear separation. Should I handle it via stratified Cox regression or using separate Log-rank test within subsets? I will use R only to illustrate. I want to ...
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### When computing period-specific hazard ratio using Cox, should I add variable:strata or full variable * strata?

Let's asusme I want to calculate separate hazards ratio in two periods, split like below. ...
1 vote