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# 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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### What is the relationship between the Harrel's C and the AUC?

I model survival outcomes using a Cox proportional hazards model and want to evaluate model fit. Harrel's concordance index C is defined as the proportion of observations that the model can order ...
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### Survival analysis: Frailty vs Sandwich variance estimators

Question Can someone answer (in as non-technical terms as possible) whether or not frailty models and robust sandwich variance estimators are trying to solve the same problem in different contexts? ...
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### How to test interaction when loglinearity is violated in Cox model?

In a Cox PH regression, I would like to model an interaction between two variables. The problem is that one of the variables breaks the log-linearity assumption. Based on my previous questions (...
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### How make distinct predictions for every observation using survreg for AFT models?

I have a life dataset where I have a few machines tested using the same parameter settings but results in different survival days. As an example below: ...
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### Left-Truncated Right-Censored Cox Proportional Hazard Regression

If I have a left-truncated (remove everyone who has disease at baseline) and right-censored (1 if the person develops disease, 0 else). Time to event = min(age censored, age at disease diagnosis) ...
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### 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 ...
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### Check hazard proportional assuption in a large coxph

I would like to check hazard proportional assuption in a large coxph. Usually I check it with cox.zph but with large coxph my p-value are very small whereas the log(-log(S(t)) curves are almost ...
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### Survival Analysis/Customer Attrition Model for Balances

I’m looking to model balance, meaning dollars, decay(attrition). In brief, I have time series customer data, which is aggregated to get customer’s balances for a specific product. Over time, the ...
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### R coxph vs. coxme: Vastly different Coefficients of Determination

Comparing comparably defined models in R's coxph() and coxme() I experienced hugely different results when calculation the Coefficient of Determination using MuMIns r.squaredLR. For the coxme()-fit ...
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### 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, ...
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### 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 ...
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### Assessing loss of different parsimony levels (Cox Model)

I have a Cox Proportional Hazard model with 6 covariates to determine OS. I am now trying to simplify this model by taking some of this covariates down. This is intended for a wide audience so I'm ...
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### Same results using time dependent covariates in Cox model as in unadjusted model?

I encountered a case where the coxph model result is exactly the same with and without time dependent covariate adjustment. I tested using the Stanford heart transplant dataset (jasa) as exampled in ...
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### How is the combined effect of explanatory variables calculated for Cox proportional hazard model? [closed]

I am just learning about the use of Cox proportional hazard model. As I understand it if I feed in the data and 2 explanatory variables, I would get the hazard ratio for each variable with the other ...
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### Survival Analysis and multiple observations

I am currently conducting a survival analysis for the first time and I am finding the conceptual aspects of the analysis a bit tricky. I have a hospitalization dataset that spans over a 20 year period ...
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### Is it suitable to fit a Cox PH model for Life Data?

I have life data where experiments are conducted at different settings to observe machine degradation. A close example of how the data looks like is from this link: http://www.statvision.com/webinars/...
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### Piecewise survival analysis?

I am trying to analyze time-to-event data (time to completion of a task). Looking at the KM curves, there is a distinct behavioral change around 12 months. This makes sense, because at 12 months there ...
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### Simulating survival data for a Cox model with a dichotomous time-varying covariate in R

I am interested in simulating non-proportional data following the formulation in Section 3.1 of the article: [Generating survival times to simulate Cox proportional hazards models with time‐varying ...
321 views

### Cox model with different follow-up times in groups

We have a dataset where the non-exposed group has follow up to 5 years but the exposed group has follow up only to 1 year (>1 year not possible in the dataset). Analysis is with Cox regression. ...
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### coxme proportional hazard assumption

I am running mixed effect Cox models (I have 1 random effect factor) using the coxme function {coxme} in R, and I would like to ...
160 views

### Interpretation of Cox Hazard Model with quadratic term

I am having trouble finding information on how to interpret coxph model hazard ratios with a quadratic term. Some of my variables are continuous count data, whereas others are continuous percentages. ...
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### How to plot the area under curve and the calibration curve for cox regression model applied to a test sample?

How to plot the area under curve and the calibration curve for cox regression model applied to a test sample using rms package? please
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### Simulate confidence intervals for the absolute difference between two hazard ratios

I am examining the time to an (recurrent) event in response to different medications between men and women. I am adopting a 'within-individual' design whereby each person's time spent on- and off- the ...
284 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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### What are easy steps of finding cutpoint in continuous variable with Time to event outcome, in Stata?

I find it painful to manually guess a dichotomized cutpoint predictor (continuous) for an time to event outcome in Simple Cox proportional hazard model. Currently I was trying to find the cutpoint ...
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### Propensity Score Matching with Cox Regression

I am conducting a survival analysis with a Cox regression whereby the outcome variable (promotion to a senior role) is either 0 or 1. I am particulalry interested in the hazard rate (i.e., the 'hazard'...
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### Finding exposures given a risk set and an MLE

I'm tackling advanced use of a Cox proportional model and I've been given the exposure times for two risk sets shown below $R_{_1}: 7,8,11,15,19$ $R_{_2}: 6,8,10,13,18$ I've also been given the ...
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### Simulation in R of data based on Cox proportional-hazards model for power analysis

I would like to fit data based on Cox proportional-hazards model and then simulate new data based on a fitted model. For instance, provided that the fit is ...
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### When doing Cox regression, what should we take as event duration for censored data, and how should we divide the data into training and testing sets?

I am starting out with survival analysis, and am confused about some things specifically in Cox regression. I have not found a tutorial that explains these things clearly, that's why I'm posting this ...
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### Cox proportional hazards: time dependent covariates with survey weights

I'm analyzing data from a survey that utilized multistage probability sampling. I'm using R and therefore the bulk of my analyses with these data utilize the survey package to account for the ...
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### 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 ...
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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 ...
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### Including a baseline risk for each participant to consider having a different number of data points in Cox model

We used the Cox model to associate environmental exposures with time to heart failure using cohort data. The following question has been raised: When using the extended Cox model, did you include a ...
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### How to better understand when to use Weibull AFT versus Cox Model for Failure Data

I am struggling to understand when I should consider using a Cox regression model versus using a Weibull AFT model to predict the end of life of mechanical components. I have tried to apply the Cox ...
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### Sample size / power calculation for logrank survival test

I have really little idea of survival analysis. I am aware that logrank is a special case of Cox' proportional hazards model, and that tons of R packages and scripts address the problem of power / ...
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### Determining sample size for proportional hazard

I am in the design phase for a longitudinal study examining the effect of a predictor (neighborhood risk score) on time to an outcome (re-arrest), as well as whether or not the variation explained by ...
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### Cox Proportional-Hazards Regression vs. Regression modeling of competing risk using Fine and Gray

30000 patients all have one diagnosis in common, 3000 of them have been exposed to a potential risk factor before the common diagnosis. 1500 patients develop a malignancy after the common diagnosis. ...
321 views

### Utilizing Extended Cox Model with repeated measures and/or time-dependent covariates + wanted end result question

I am working on a survival analysis that looks at time-independent as well as time-dependent variables. I have been reading at length the use of time-dependent variables, which requires an Extended ...
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### How to obtain predicted time to event using survival analysis?

I have a dataset with right censored data and I have fitted a cox regression model on it but I realised that the output of the model is a hazard rate rather than a prediction of time to event. I have ...
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### Why and how does adding an interaction term affects the confidence interval of a main effect?

I was wondering why, in a regression model including an interaction term, the confidence interval of one of the main effects becomes wider. Consider this Cox regression, where the variable IR_BMI27 ...
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### Attirbutable risk from competing risks

There are a number of ways to estimate attributable risk fractions from Cox regression and logistic regression. Does anyone know how to estimate attributable risk from a competing risks regression ...
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### log values in coxph model?

I have a data frame of gene expression values (sequencing). When I do CPM-normalization without doing log2, I get much "better" (lower) p-values compared to when I do log2-CPM. What is the ...
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### proportional hazards model with fixed interval censoring = cloglog GLM with fixed effect of time?

Consider a survival analysis with time-constant coefficients, interval-censored, where the observation intervals are consistent across all individuals (e.g. each individual is observed at the end of ...
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### Comparing different methods of discrete-time survival analysis

I'm investigating a discrete time survival problem (the units are months and exit times range from month 1 to 36). From looking around so far, it seems like there are a few different types of model ...
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### What does the output of a Cox Proportional Hazard model mean?

For a linear regression plugging different X values to the fitted model gives us the different predicted Y values, for a logistic regression we get the different log odds: what does the output of the ...
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### Multiple cox regression with no events in one group of one variable — survival analysis

I am trying to run a multivariate Cox regression analysis but I have 1 value for 1 variable that has no events reached. This variable was treatment (values = treatment 1, treatment 2, treatment 3, and ...
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### Simulate recurrent events data where last observation is censored

I would like to simulate a recurrent events dataset for survival analysis with cox regression in R. The data should have the following properties: multiple, varying number of observations per ID only ...